Research activity information

• Feb. 2021 米国物理学会 Physical Review D, Editors's Suggestion

  ``Noise and decoherence induced by gravitons", Sugumi Kanno, Jiro Soda, Junsei Tokuda


• Jul. 2019 日本学術振興会, 特別研究員等審査会専門委員表彰

  早田 次郎


• Sep. 2016 日本学術振興会, 平成28年度「科研費」審査委員表彰

  早田 次郎


• Mar. 2016 日本物理学会, 第２１回論文賞, The Nature of Primordial Fluctuations from Anisotropic Inflation


• 2012 IOP, Classical and Quantum Gravity, Highlights of 2011-2012, Statistical Anisotropy from Anisotropic Inflation

  Soda Jiro


• 2010 大和日英基金, 大和エイドリアン賞

  早田 次郎


• Jan. 2010 Yukawa Memorial Foundation, Yukawa-Kimura prize, Cosmology and black holes in higher dimensional gravity

  Soda Jiro

• Circularly polarized gravitational waves in Chern-Simons gravity originating from an axion domain wall

  Sugumi Kanno, Jiro Soda, Akira Taniguchi

  American Physical Society (APS), Oct. 2023, Physical Review D, 108(8) (8)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• A peak in the power spectrum of primordial gravitational waves induced by primordial dark magnetic fields

  Sugumi Kanno, Ann Mukuno, Jiro Soda, Kazushige Ueda

  Abstract Dark gauge fields have been discussed as candidates for dark matter recently. If they existed, primordial dark magnetic fields during inflation would have existed. It is believed that primordial gravitational waves (PGWs) arise out of quantum fluctuations during inflation. We study the graviton-dark photon conversion process in the presence of background primordial dark magnetic fields and find that the process induces the tachyonic instability of the PGWs. As a consequence, a peak appears in the power spectrum of PGWs. It turns out that the peak height depends on the direction of observation. The peak frequency could be in the range from 10^-5 to 10³ Hertz for GUT scale inflation. Hence, the observation of PGWs could provide a new window for probing primordial dark magnetic fields.

  IOP Publishing, May 2023, Journal of Cosmology and Astroparticle Physics, 2023(05) (05), 052 - 052

  Scientific journal


• Conversion of squeezed gravitons into photons during inflation

  Sugumi Kanno, Jiro Soda, Kazushige Ueda

  American Physical Society (APS), Oct. 2022, Physical Review D, 106(8) (8)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Squeezed quantum states of graviton and axion in the universe

  Sugumi Kanno, Jiro Soda

  Particle production during cosmic expansion can be interpreted as a two-mode squeezing process of quantum states. The two-mode squeezed states consist of an infinite number of entangled particles and then enhance the nonclassicality of particles. There are two methods for estimating the degree of squeezing. One is to employ instantaneous vacuum states, and the other is to adopt adiabatic vacuum states. We analytically study the squeezing process of gravitons and axions by using the two methods. We first consider a cosmological model of inflation followed by instantaneous reheating leading to a radiation dominated era. In the case of gravitons, we find no qualitatively difference in the squeezing between the two methods. However, for the axions, it turns out that the squeezing in the instantaneous vacuum increases as the mass increases while the squeezing decreases in the adiabatic vacuum as the mass increases. We then study the effect of noninstantaneous reheating on the the squeezing and show that the squeezing is enhanced compared with the instantaneous reheating. We also illustrate how the squeezed states enhance the violation of Bell inequality and quantum noise of gravitons and axions.

  World Scientific Pub Co Pte Ltd, Aug. 2022, International Journal of Modern Physics D, 31(13) (13)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Axion search with quantum nondemolition detection of magnons

  Tomonori Ikeda, Asuka Ito, Kentaro Miuchi, Jiro Soda, Hisaya Kurashige, Yutaka Shikano

  American Physical Society (APS), May 2022, Physical Review D, 105(10) (10)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Harvesting quantum coherence from axion dark matter

  Sugumi Kanno, Akira Matsumura, Jiro Soda

  Quantum coherence is one of the most striking features of quantum mechanics rooted in the superposition principle. Recently, it has been demonstrated that it is possible to harvest the quantum coherence from a coherent scalar field. In order to explore a new method of detecting axion dark matter, we consider a point-like Unruh–DeWitt detector coupled to the axion field and quantify a coherent measure of the detector. We show that the detector can harvest the quantum coherence from the axion dark matter. To be more precise, we consider a two-level electron system in an atom as the detector. In this case, we obtain the coherence measure [Formula: see text] where [Formula: see text] and [Formula: see text] are an observation time and the Lorentz factor. At the same time, the axion mass [Formula: see text] we can probe is determined by the energy gap of the detector.

  World Scientific Pub Co Pte Ltd, Feb. 2022, Modern Physics Letters A, 37(05) (05)

  Scientific journal


• Indirect detection of gravitons through quantum entanglement

  Sugumi Kanno, Jiro Soda, Junsei Tokuda

  American Physical Society (APS), Oct. 2021, Physical Review D, 104(8) (8)

  Scientific journal


• Nano-Hz Gravitational-Wave Signature from Axion Dark Matter

  Naoya Kitajima, Jiro Soda, Yuko Urakawa

  American Physical Society (APS), Mar. 2021, Physical Review Letters, 126(12) (12)

  [Refereed]

  Scientific journal


• O(d,d;Z) invariant Fierz-Pauli massive gravity

  Toshifumi Noumi, Kaishu Saito, Jiro Soda, Daisuke Yoshida

  American Physical Society (APS), Feb. 2021, Physical Review D, 103(4) (4)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Noise and decoherence induced by gravitons

  Sugumi Kanno, Jiro Soda, Junsei Tokuda

  American Physical Society (APS), Feb. 2021, Physical Review D, 103(4) (4)

  Scientific journal


• Search for ultralight scalar dark matter with NANOGrav pulsar timing arrays

  Ryo Kato, Jiro Soda

  IOP Publishing Ltd, Sep. 2020, Journal of Cosmology and Astroparticle Physics, 2020(9) (9), English

  Scientific journal


• Effective field theory of anisotropic inflation and beyond

  Jinn-Ouk Gong, Toshifumi Noumi, Gary Shiu, Jiro Soda, Kazufumi Takahashi, Masahide Yamaguchi

  IOP Publishing, Aug. 2020, Journal of Cosmology and Astroparticle Physics, 2020(08) (08), 027 - 027

  [Refereed]

  Scientific journal


• A formalism for magnon gravitational wave detectors

  Asuka Ito, Jiro Soda

  Springer, Jun. 2020, European Physical Journal C, 80(6) (6), English

  Scientific journal


• Polarized Initial States of Primordial Gravitational Waves

  Sugumi Kanno, Jiro Soda

  Polarizations of primordial gravitational waves can be relevant when considering an inflationary universe in modified gravity or when matter fields survive during inflation. Such polarizations have been discussed in the Bunch–Davies vacuum. Instead of taking into account the dynamical generation of polarizations of gravitational waves, in this paper, we consider polarized initial states constructed from S U ( 2 ) coherent states. We then evaluate the power spectrums of the primordial gravitational waves in the states.

  MDPI AG, Apr. 2020, Symmetry, 12(4) (4), 672 - 672

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Probing GHz gravitational waves with graviton–magnon resonance

  Asuka Ito, Tomonori Ikeda, Kentaro Miuchi, Jiro Soda

  Abstract A novel method for extending the frequency frontier in gravitational wave observations is proposed. It is shown that gravitational waves can excite a magnon. Thus, gravitational waves can be probed by a graviton–magnon detector which measures resonance fluorescence of magnons. Searching for gravitational waves with a wave length$$\lambda $$by using a ferromagnetic sample with a dimensionl, the sensitivity of the graviton–magnon detector reaches spectral densities, around$$5.4 \times 10^{-22} \times (\frac{l},{\lambda /2\pi })^{-2} \ [\mathrm{Hz}^{-1/2}]$$at 14 GHz and$$8.6 \times 10^{-21} \times (\frac{l},{\lambda /2\pi })^{-2} \ [\mathrm{Hz}^{-1/2}]$$at 8.2 GHz, respectively.

  Springer Science and Business Media LLC, Feb. 2020, The European Physical Journal C, 80(3) (3)

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Stability of axion dark matter-photon conversion

  Emi Masaki, Arata Aoki, Jiro Soda

  American Physical Society, Feb. 2020, Physical Review D, 101(4) (4), English

  Scientific journal


• Birth of de Sitter universe from a time crystal universe

  Daisuke Yoshida, Jiro Soda

  American Physical Society, Dec. 2019, Physical Review D, 100(12) (12), English

  Scientific journal


• Accelerating Universe with a stable extra dimension in cuscuton gravity

  Asuka Ito, Yuki Sakakihara, Jiro Soda

  We study Kaluza-Klein cosmology in cuscuton gravity and find an exact solution describing an accelerating 4-dimensional universe with a stable extra dimension. A cuscuton which is a non-dynamical scalar field is responsible for the accelerating expansion and a vector field makes the extra dimensional space stable. Remarkably, the accelerating universe in our model is not exactly de Sitter.

  Jun. 2019

  Link to Kobe Univ. Repository (Kernel)


• Electromagnetic waves propagating in the string axiverse

  Daiske Yoshida, Jiro Soda

  Physical Society of Japan, Apr. 2018, Progress of Theoretical and Experimental Physics, 2018(4) (4), 041E01, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Separability of equations of form field in schwartzschild spacetime

  Daiske Yoshida, Jiro Soda

  Rikkyo University, 2018, Proceedings of the 28th Workshop on General Relativity and Gravitation in Japan, JGRG 2018, 3, 84 - 85, English

  International conference proceedings


• A strategy for detecting the bispectrum of stochastic gravitational waves

  Asuka Ito, Tsuneto Makoto, Toshifumi Noumi, Jiro Soda

  Rikkyo University, 2018, Proceedings of the 28th Workshop on General Relativity and Gravitation in Japan, JGRG 2018, 1, 68 - 80, English

  International conference proceedings


• Searching for Bispectrum of Stochastic Gravitational Waves with Pulsar Timing Arrays

  MAKOTO Tsuneto, ITO Asuka, NOUMI Toshifumi, SODA Jiro

  2018, JCAP, 1903(03) (03), 032, English

  [Refereed]

  Scientific journal


• Quasinormal modes of p-forms in spherical black holes

  YOSHIDA Daiske, SODA Jiro

  2018, Phys.Rev., D99, 044054, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Gravitational Wave Forest from String Axiverse

  N. Kitajima, SODA Jiro

  2018, JCAP, 1810(008) (008), English

  [Refereed]

  Scientific journal


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  YOSHIDA Daiske, SODA Jiro

  2018, Int.J.Mod.Phys., D27(09) (09), 1850096, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Dressed Power-law Inflation with Cuscuton,

  ITO Asuka, IYONAGA Aya, KIM Suro, SODA Jiro

  2018, Phys.Rev., D99(083502) (083502), English

  [Refereed]

  Scientific journal


• Detecting nonclassical primordiall gravitational waves with Hanbury-Brown-Twiss interfereometry

  S. Kanno, SODA Jiro

  2018, Phys.Rev., D99, 084010, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Cosmological Imprints of String Axions in Plateau

  SODA Jiro, Y. Urakawa

  2018, Eur.Phys.J., C78, 041E01, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Conversion of Gravitons into Dark Photons in Cosmological Dark Magnetic Fields

  MASAKI Emi, SODA Jiro

  2018, Phys.Rev., D98(023540) (023540), English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Exploring string axions with gravitational waves

  Jiro Soda, Daiske Yoshida

  MDPI AG, Dec. 2017, Galaxies, 5(4) (4), 96, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Stability of squashed Kaluza-Klein black holes (vol 77, 064015, 2008)

  Masashi Kimura, Keiju Murata, Hideki Ishihara, Jiro Soda

  Oct. 2017, PHYSICAL REVIEW D, 96(8) (8), English


• Infinite violation of Bell inequalities in inflation

  Sugumi Kanno, Jiro Soda

  Oct. 2017, PHYSICAL REVIEW D, 96(8) (8), 083501, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Electromagnetic memory effect induced by axion dark matter

  Daiske Yoshida, Jiro Soda

  Sep. 2017, PHYSICAL REVIEW D, 96(6) (6), 064005, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Primordial gravitational waves induced by magnetic fields inanekpyrotic scenario

  Asuka Ito, Jiro Soda

  Aug. 2017, PHYSICS LETTERS B, 771, 415 - 420, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Photon-axion conversion, magnetic field configuration, and polarization of photons

  Emi Masaki, Arata Aoki, Jiro Soda

  Aug. 2017, PHYSICAL REVIEW D, 96(4) (4), English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Nonlinear resonant oscillation of gravitational potential induced by ultralight axion in f (R) gravity

  Arata Aoki, Jiro Soda

  Jul. 2017, PHYSICAL REVIEW D, 96(2) (2), English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Nonlinear resonant oscillation of gravitational potential induced by ultralight axion in f (R) gravity

  Arata Aoki, Jiro Soda

  Jul. 2017, PHYSICAL REVIEW D, 96(2) (2), 023534, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Detecting ultralight axion dark matter wind with laser interferometers

  Arata Aoki, Jiro Soda

  Jun. 2017, INTERNATIONAL JOURNAL OF MODERN PHYSICS D, 26(7) (7), English

  [Refereed]

  Scientific journal


• Primordial gravitational waves and early universes

  Asuka Ito, Jiro Soda

  Hiroshima University, 2017, Proceedings of the 27th Workshop on General Relativity and Gravitation in Japan, JGRG 2017, 2, 322 - 330, English

  International conference proceedings


• Quantum Correlations in de Sitter Space

  Soda Jiro, Kanno Sugumi, Shock Jonathan P.

  MDPI, Jan. 2017, Universe, 3(1) (1), 2 - 2, English

  Link to Kobe Univ. Repository (Kernel)


• Schwinger Pair Production by Electric Field Coupled to Inflation

  J.J.Geng,B.Li, SODA Jiro, A.Wang, Q.WuT.Zhu

  2017, JCAP, 1802, 018, English

  [Refereed]

  Scientific journal


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  SODA Jiro, YOSHIDA Daisuke

  2017, Int. J. Mod. Phys, D, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Electromagnetic waves propagating in the string axiverse

  SODA Jiro, YOSHIDA Daisuke

  2017, PTEP 2018, (4) (4), 041E01, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Bell inequality and its application to cosmology

  菅野 優美, SODA Jiro

  2017, Galaxies, 5, 99, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Anisotropic constant-roll inflation

  AOKI Arata, SODA Jiro

  2017, Eur.Phys.J, C78(1) (1), 55, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Quantum discord in de Sitter space

  Sugumi Kanno, Jonathan P. Shock, Jiro Soda

  Dec. 2016, PHYSICAL REVIEW D, 94(12) (12), English

  [Refereed]

  Scientific journal


• Oscillating chiral tensor spectrum from axionic inflation

  Ippei Obata, Jiro Soda

  Aug. 2016, PHYSICAL REVIEW D, 94(4) (4), English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Chiral primordial gravitational waves from dilaton induced delayed chromonatural inflation

  Ippei Obata, Jiro Soda

  Jun. 2016, PHYSICAL REVIEW D, 93(12) (12), English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Pulsar timing signal from ultralight axion in f(R) theory

  Arata Aoki, Jiro Soda

  Apr. 2016, PHYSICAL REVIEW D, 93(8) (8), 083503, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• MHz gravitational waves from short-term anisotropic inflation

  Asuka Ito, Jiro Soda

  Apr. 2016, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, (4) (4), English

  [Refereed]

  Scientific journal


• Probing circular polarization in stochastic gravitational wave background with pulsar timing arrays

  Ryo Kato, Jiro Soda

  Mar. 2016, PHYSICAL REVIEW D, 93(6) (6), 062003, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Comment on "Gauss-Bonnet inflation"

  Getbogi Hikmawan, Jiro Soda, Agus Suroso, Freddy P. Zen

  Mar. 2016, PHYSICAL REVIEW D, 93(6) (6), 068301, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Quasinormal modes of black holes in Lovelock gravity

  Daiske Yoshida, Jiro Soda

  Feb. 2016, PHYSICAL REVIEW D, 93(4) (4), 044024, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Designing anisotropic inflation with form fields

  Asuka Ito, Jiro Soda

  Dec. 2015, PHYSICAL REVIEW D, 92(12) (12), 123533, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Primordial gravitational waves in bimetric gravity

  Yuki Sakakihara, Jiro Soda

  Sep. 2015, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 1509(9) (9), 015, English

  [Refereed]

  Scientific journal


• Chromo-natural inflation in the axiverse

  Ippei Obata, Takashi Miura, Jiro Soda

  Sep. 2015, PHYSICAL REVIEW D, 92(6) (6), 063516, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Quasi-normal modes of lovelock black hole

  Daisuke Yoshida, Jiro Soda

  Kyoto University, Yukawa Institute for Theoretical Physics, 2015, Proceedings of the 25th Workshop on General Relativity and Gravitation in Japan, JGRG 2015, 3, 626 - 632, English

  International conference proceedings


• Detection of circular polarization in stochastic gravitational wave background with pulsar timing arrays

  Ryo Kato, Jiro Soda

  Kyoto University, Yukawa Institute for Theoretical Physics, 2015, Proceedings of the 25th Workshop on General Relativity and Gravitation in Japan, JGRG 2015, 5, 1262 - 1263, English

  International conference proceedings


• Anisotropic Power-law Inflation: A counter example to the cosmic no-hair conjecture

  Soda Jiro

  Conference: Spanish Relativity Meeting (ERE2014): almost 100 years after Einstein's revolution

  IOP Publishing, 2015, Journal of Physics: Conference Series, 600, 12026 - 12026, English

  Link to Kobe Univ. Repository (Kernel)


• Dynamics of electroweak gauge fields during and after Higgs inflation

  Ippei Obata, Takashi Miura, Jiro Soda

  Aug. 2014, PHYSICAL REVIEW D, 90(4) (4), 045005, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• Entanglement entropy of alpha-vacua in de Sitter space

  Sugumi Kanno, Jeff Murugan, Jonathan P. Shock, Jiro Soda

  Jul. 2014, JOURNAL OF HIGH ENERGY PHYSICS, 1407(7) (7), 072, English

  [Refereed]

  Scientific journal


• Schwinger effect in de Sitter space

  Markus B. Froeb, Jaume Garriga, Sugumi Kanno, Misao Sasaki, Jiro Soda, Takahiro Tanaka, Alexander Vilenkin

  Apr. 2014, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 1404(4) (4), 009, English

  [Refereed]

  Scientific journal


• Tensor spectrum in bimetric gravity

  Yuki Sakakihara, Jiro Soda

  University of Tokyo, Kavli Institute for Physics and Mathematics of the Universe, KIPMU, 2014, JGRG 2014 - Proceedings of the 24th Workshop on General Relativity and Gravitation in Japan, 2, 253 - 260, English

  International conference proceedings


• Entanglement negativity in the multiverse

  S Kanno, J Shock, J Soda

  2014, JCAP, 1503, 015, English

  [Refereed]

  Scientific journal


• Observational signatures of anisotropic inflationary models

  Junko Ohashi, Jiro Soda, Shinji Tsujikawa

  Dec. 2013, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 12(009) (009), 1 - 30, English

  [Refereed]


• Anisotropic power-law k-inflation

  Junko Ohashi, Jiro Soda, Shinji Tsujikawa

  Nov. 2013, Physical Review D - Particles, Fields, Gravitation and Cosmology, 88(10) (10), 103517, English

  [Refereed]

  Scientific journal

  Link to Kobe Univ. Repository (Kernel)


• “An inflationary universe in weyl gauge theory of gravitation”

  Masaaki Watanabe, Jiro Soda

  Hirosaki University, 2013, JGRG 2013 - Proceedings of the 23rd Workshop on General Relativity and Gravitation in Japan, 2, 337 - 347, English

  International conference proceedings


• On Cosmic No-hair in Bimetric Gravity and the Higuchi Bound

  Yuki Sakakihara, Jiro Soda, Tomohiro Takahashi

  We study the cosmic no-hair in the presence of spin-2 matter, i.e. in bimetric gravity. We obtain stable de Sitter solutions with the cosmological constant in the physical sector and find an evidence that the cosmic no-hair is correct. In the presence of the other cosmological constant, there are two branches of de Sitter solutions. Under anisotropic perturbations, one of them is always stable and there is no violation of the cosmic no-hair at the linear level. The stability of the other branch depends on parameters and the cosmic no-hair can be violated in general. Remarkably, the bifurcation point of two branches exactly coincides with the Higuchi bound. It turns out that there exists a de Sitter solution for which the cosmic no-hair holds at the linear level and the effective mass for the anisotropic perturbations is above the Higuchi bound.

  Nov. 2012


• Inflation with multi-vector hair: the fate of anisotropy

  Kei Yamamoto, Masa-aki Watanabe, Jiro Soda

  Jul. 2012, CLASSICAL AND QUANTUM GRAVITY, 29(14) (14), 5008, English

  [Refereed]

  Scientific journal


• Pathologies in Lovelock AdS black branes and AdS/CFT

  Takahashi Tomohiro, Soda Jiro

  We study pathologies in AdS black branes in Lovelock theory. More precisely, we examine the conditions that AdS black branes have a naked singularity, ghost instability and dynamical instability. From the point of view of the AdS/CFT correspondence, pathologies in AdS black branes indicate pathologies in the corresponding CFT. Hence, in Lovelock theory, we need to be careful when we apply AdS/CFT to various phenomena such as the shear viscosity to entropy ratio in strongly coupled quantum field theory.

  IOP Publishing, Feb. 2012, Classical and Quantum Gravity, 29(3) (3), English


• Inflation in bimetric gravity

  Yuki Sakakihara, Jiro Soda, Tomohiro Takahashi

  2012, RESCEU Symposium on General Relativity and Gravitation, JGRG 22, 111425, English

  International conference proceedings


• Observer dependence of bubble nucleation and Schwinger pair production

  J. Garriga, S. Kanno, M. Sasaki, J. Soda, A. Vilenkin

  2012, Journal of Cosmology and Astroparticle Physics, 2012(12) (12), English

  [Refereed]


• Destabilizing tachyonic vacua at or above the BF bound

  S. Kanno, M. Sasaki, J. Soda

  It is well known that tachyonic vacua in an asymptotically Anti-de Sitter (AdS) spacetime are classically stable if the mass squared is at or above the Breitenlohner and Freedman (BF) bound. We study the quantum stability of these tachyonic vacua in terms of instantons. We find a, series of exact instanton solutions destabilizing tachyonic state at or above the BF bound in asymptotically AdS space. We also give an analytic formula for the decay rate and show that it is finite. Comparing our result with the well-known algebraic condition for the stability, we discuss stability conditions of tachyonic vacua at or above the BF bound.

  Publication Office, Progress of Theoretical Physics, 2012, Progress of Theoretical Physics, 128(1) (1), 213 - 226, English

  [Refereed]


• Tunneling without barriers with gravity

  S. Kanno, M. Sasaki, J. Soda

  2012, Classical and Quantum Gravity, 29(7) (7), English

  [Refereed]


• Holographic dual of de Sitter universe with AdS bubbles

  S. Kanno, M. Sasaki, J. Soda

  2012, Nuclear Physics B, 855(2) (2), 361 - 387, English

  [Refereed]


• Exact Coleman-de Luccia Instantons

  Sugumi Kanno, Jiro Soda

  We present exact Coleman-de Luccia (CdL) instantons, which describe vacuum decay from Anti de Sitter (AdS) space, de Sitter (dS) space and Minkowski space to AdS space. We systematically obtain these exact solutions by considering deformation of Hawking-Moss (HM) instantons. We analytically calculate decay rates and discuss a subtlety in the interpretation.

  Nov. 2011

  [Refereed]


• Parity Violation in Graviton Non-gaussianity

  Jiro Soda, Hideo Kodama, Masato Nozawa

  We study parity violation in graviton non-gaussianity generated during inflation. We develop a useful formalism to calculate graviton non-gaussianity. Using this formalism, we explicitly calculate the parity violating part of the bispectrum for primordial gravitational waves in the exact de Sitter spacetime and prove that no parity violation appears in the non-gaussianity. We also extend the analysis to slow-roll inflation and find that the parity violation of the bispectrum is proportional to the slow-roll parameter. We argue that parity violating non-gaussianity can be tested by the CMB. Our results are also useful for calculating three-point function of the stress tensor in the non-conformal field theory through the gravity/field theory correspondence.

  Springer, Jun. 2011, Journal of High Energy Physics, 2011(8) (8), 1 - 22

  Scientific journal


• Anisotropic inflation with non-abelian gauge kinetic function

  Keiju Murata, Jiro Soda

  Jun. 2011, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, (6) (6), English

  [Refereed]

  Scientific journal


• Imprints of anisotropic inflation on the cosmic microwave background

  Masa-aki Watanabe, Sugumi Kanno, Jiro Soda

  We study the imprints of anisotropic inflation on the CMB temperature fluctuations and polarizations. The statistical anisotropy stems not only from the direction dependence of curvature and tensor perturbations, but also from the cross correlation between curvature and tensor perturbations, and the linear polarization of tensor perturbations. We show that off-diagonal $TB$ and $EB$ spectrum as well as on- and off-diagonal $TT, EE, BB, TE$ spectrum are induced from anisotropic inflation. We emphasize that the off-diagonal spectrum induced by the cross correlation could be a characteristic signature of anisotropic inflation.

  Nov. 2010

  [Refereed]


• Master Equations for Gravitational Perturbations of Static Lovelock Black Holes in Higher Dimensions

  Tomohiro Takahashi, Jiro Soda

  Nov. 2010, PROGRESS OF THEORETICAL PHYSICS, 124(5) (5), 911 - 924, English

  [Refereed]

  Scientific journal


• Anisotropic Power-law Inflation

  Sugumi Kanno, Jiro Soda, Masa-aki Watanabe

  We study an inflationary scenario in supergravity model with a gauge kinetic function. We find exact anisotropic power-law inflationary solutions when both the potential function for an inflaton and the gauge kinetic function are exponential type. The dynamical system analysis tells us that the anisotropic power-law inflation is an attractor for a large parameter region.

  Oct. 2010

  [Refereed]


• Catastrophic Instability of Small Lovelock Black Holes(Astrophysics and Cosmology)

  Tomohiro TAKAHASHI, Jiro SODA, Department of Physics Kyoto University, Department of Physics Kyoto University

  We study the stability of static black holes in Lovelock theory which is a natural higher dimensional generalization of Einstein theory. We show that Lovelock black holes are stable under vector perturbations in all dimensions. However, we prove that small Lovelock black holes are unstable under tensor perturbations in even dimensions and under scalar perturbations in odd dimensions. Therefore, we can conclude that small Lovelock black holes are unstable in any dimensions. The instability is stronger on small scales and hence catastrophic in the sense that there is no smooth descendant.

  Publication Office, Progress of Theoretical Physics, Oct. 2010, Progress of theoretical physics = Progress of theoretical physics, 124(4) (4), 711 - 729, English


• Hawking radiation from fluctuating black holes

  Takahashi Tomohiro, Soda Jiro

  Classically, black holes have a rigid event horizon. However, quantum mechanically, the event horizon of black holes becomes fuzzy due to quantum fluctuations. We study Hawking radiation of a real scalar field from a fluctuating black hole. To quantize metric perturbations, we derive the quadratic action for those in the black hole background. Then, we calculate cubic interaction terms in the action for the scalar field. Using these results, we obtain the spectrum of Hawking radiation in the presence of the interaction between the scalar field and the metric. It turns out that the spectrum deviates from the Planck spectrum due to quantum fluctuations of the metric.

  IOP Publishing Ltd., Sep. 2010, Classical and Quantum Gravity, 27(17) (17), English


• Stability of Holographic Superconductors

  Sugumi Kanno, Jiro Soda

  We study the dynamical stability of holographic superconductors. We first classify perturbations around black hole background solutions into vector and scalar sectors by means of a 2-dimensional rotational symmetry. We prove the stability of the vector sector by explicitly constructing the positive definite Hamiltonian. To reveal a mechanism for the stabilization of a superconducting phase, we construct a quadratic action for the scalar sector. From the action, we see the stability of black holes near a critical point is determined by the equation of motion for a charged scalar field. We show the effective mass of the charged scalar field in hairy black holes is always above the Breitenlohner-Freedman bound near the critical point due to the backreaction of a gauge field. It implies the stability of the superconducting phase. We also argue that the stability continues away from the critical point.

  Jul. 2010

  [Refereed]


• The Nature of Primordial Fluctuations from Anisotropic Inflation(Astrophysics and Cosmology)

  Masa-aki WATANABE, Sugumi KANNO, Jiro SODA, Department of Physics Kyoto University, Centre for Particle Theory Department of Mathematical Sciences Durham University Science Laboratories, Department of Physics Kyoto University

  We study the statistical nature of primordial fluctuations from an anisotropic inflation which is realized by a vector field coupled to an inflaton. We find a suitable gauge, which we call the canonical gauge, for anisotropic inflation by generalizing the flat slicing gauge in conventional isotropic inflation. Using the canonical gauge, we reveal the structure of the couplings between curvature perturbations, vector waves, and gravitational waves. We identify two sources of anisotropy, i.e. the anisotropy due to the anisotropic expansion of the universe and that due to the anisotropic couplings among variables. It turns out that the latter effect is dominant. Since the coupling between the curvature perturbations and vector waves is the strongest one, the statistical anisotropy in the curvature perturbations is larger than that in gravitational waves. We find the cross correlation between the curvature perturbations and gravitational waves which never occurs in conventional inflation. We also find the linear polarization of gravitational waves. Finally, we discuss cosmological implication of our results.

  Publication Office, Progress of Theoretical Physics, Jun. 2010, Progress of theoretical physics = Progress of theoretical physics, 123(6) (6), 1041 - 1068, English


• Linear instability of lovelock black holes

  Tomohiro Takahashi, Jiro Soda

  2010, Proceedings of the 20th Workshop on General Relativity and Gravitation in Japan, JGRG 2010, 387 - 390, English

  International conference proceedings


• Instability of small Lovelock black holes in even dimensions

  Tomohiro Takahashi, Jiro Soda

  Nov. 2009, Physical Review D - Particles, Fields, Gravitation and Cosmology, 80(10) (10), English

  Scientific journal


• Cosmological Magnetic Fields from Inflation and Backreaction

  Sugumi Kanno, Jiro Soda, Masa-aki Watanabe

  We study the backreaction problem in a mechanism of magnetogenesis from inflation. In usual analysis, it has been assumed that the backreaction due to electromagnetic fields spoils inflation once it becomes important. However, there exists no justification for this assumption. Hence, we analyze magnetogenesis from inflation by taking into account the backreaction. On the contrary to the naive expectation, we show that inflation still continues even after the backreaction begins to work. Nevertheless, it turns out that creation of primordial magnetic fields is significantly suppressed due to the backreaction.

  Aug. 2009

  [Refereed]


• Holographic Superconductors with Higher Curvature Corrections

  Ruth Gregory, Sugumi Kanno, Jiro Soda

  We study (3+1)-dimensional holographic superconductors in Einstein-Gauss-Bonnet gravity both numerically and analytically. It is found that higher curvature corrections make condensation harder. We give an analytic proof of this result, and directly demonstrate an analytic approximation method that explains the qualitative features of superconductors as well as giving quantitatively good numerical results. We also calculate conductivity and $\omega_g / T_c $, for $\omega_g$ and $T_c$ the gap in the frequency dependent conductivity and the critical temperature respectively. It turns out that the `universal' behaviour of conductivity, $\omega_g / T_c \simeq 8$, is not stable to the higher curvature corrections. In the appendix, for completeness, we show our analytic method can also explain (2+1)-dimensional superconductors.

  Jul. 2009

  [Refereed]


• Chiral Primordial Gravitational Waves from a Lifshitz Point

  Tomohiro Takahashi, Jiro Soda

  Jun. 2009, PHYSICAL REVIEW LETTERS, 102(23) (23), 1 - 231301, English

  [Refereed]

  Scientific journal


• Stability of Lovelock black holes under tensor perturbations

  Tomohiro Takahashi, Jiro Soda

  May 2009, Physical Review D - Particles, Fields, Gravitation and Cosmology, 79(10) (10), English

  Scientific journal


• Inflationary Universe with Anisotropic Hair

  Masa-aki Watanabe, Sugumi Kanno, Jiro Soda

  May 2009, PHYSICAL REVIEW LETTERS, 102(19) (19), 1 - 191302, English

  [Refereed]

  Scientific journal


• Looking at the Gregory-Laflamme instability through quasinormal modes

  R. A. Konoplya, Keiju Murata, Jiro Soda, A. Zhidenko

  Oct. 2008, PHYSICAL REVIEW D, 78(8) (8), English

  [Refereed]

  Scientific journal


• Stability of five-dimensional Myers-Perry black holes with equal angular momenta

  Keiju Murata, Jiro Soda

  Sep. 2008, Progress of Theoretical Physics, 120(3) (3), 561 - 579, English

  [Refereed]

  Scientific journal


• Anisotropic Inflation from Vector Impurity

  Kanno Sugumi, Kimura Masashi, Soda Jiro, Yokoyama Shuichiro

  We study an inflationary scenario with a vector impurity. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by the vector. Using the slow-roll approximation, we find a formula to determine anisotropy of the inflationary universe. We discuss possible observable predictions of this scenario. In particular, it is stressed that primordial gravitational waves can be induced from curvature perturbations. Hence, even in low scale inflation, a sizable amount of primordial gravitational waves may be produced during

  Jun. 2008, JCAP, 0808, 034

  [Refereed]


• Primordial statistical anisotropy generated at the end of inflation

  Shuichiro Yokoyama, Jiro Soda

  May 2008, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, (8) (8), English

  [Refereed]


• Evolution of perturbations of squashed Kaluza-Klein black holes: Escape from instability

  Hideki Ishihara, Masashi Kimura, Roman A. Konoplya, Keiju Murata, Jiro Soda, Alexander Zhidenko

  Apr. 2008, PHYSICAL REVIEW D, 77(8) (8), English

  Scientific journal


• Stability of squashed Kaluza-Klein black holes

  Masashi Kimura, Keiju Murata, Hideki Ishihara, Jiro Soda

  Mar. 2008, PHYSICAL REVIEW D, 77(6) (6), English

  Scientific journal


• On the separability of field equations in Myers-Perry spacetimes

  Keiju Murata, Jiro Soda

  Feb. 2008, CLASSICAL AND QUANTUM GRAVITY, 25(3) (3), English

  [Refereed]

  Scientific journal


• Higher curvature corrections to primordial fluctuations in slow-roll inflation

  Masaki Satoh, Jiro Soda

  2008, Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan, JGRG 2008, English

  International conference proceedings


• Hawking radiation from squashed Kaluza-Klein black holes: A window to extra dimensions

  Hideki Ishihara, Jiro Soda

  Sep. 2007, PHYSICAL REVIEW D, 76(6) (6), English

  Scientific journal


• Circular Polarization of Primordial Gravitational Waves in String-inspired Inflationary Cosmology

  Masaki Satoh, Sugumi Kanno, Jiro Soda

  We study a mechanism to produce the circular polarization of primordial gravitational waves. The circular polarization is generated during the super-inflation driven by the Gauss-Bonnet term in the string-inspired cosmology. The instability in the tensor mode caused by the Gauss-Bonnet term and the parity violation due to the gravitational Chern-Simons term are the essential ingredients of the mechanism. We also discuss detectability of the produced circular polarization of gravitational waves. It turns out that the simple model of single-field inflation contradicts CMB observations. To circumvent this difficulty, we propose a two-field inflation model. In this two-field model, the circular polarization of gravitational waves is created in the frequency range designed by the Big-Bang Observer (BBO) or the deci-hertz gravitational-wave observatory (DECIGO).

  Jun. 2007

  [Refereed]


• Fate of Kaluza-Klein Black Holes: Evaporation or Excision?

  Keiju Murata, Jiro Soda, Sugumi Kanno

  We study evaporation process of black strings which are typical examples of Kaluza-Klein black holes. Taking into account the backreaction of the Hawking radiation, we deduce the evolution equation for the radion field. By solving the evolution equation, we find that the shape of the internal space is necked by the Hawking radiation and the amount of the deformation becomes large as the evaporation proceeds. Based on this analysis, we speculate that the Kaluza-Klein black holes would be excised from the Kaluza-Klein spacetime before the onset of the Gregory-Laflamme instability and therefore before the evaporation.

  Mar. 2007

  [Refereed]


• Evidence for the stability of 5-Dimensional myers-Perry black holes with equal angular momenta

  Keiju Murata, Jiro Soda

  2007, Proceedings of the 17th Workshop on General Relativity and Gravitation in Japan, JGRG 2007, 269 - 272, English

  International conference proceedings


• Circular polarization of primordial gravitational waves due to stringy effects

  Masaki Satoh, Jiro Soda, Sugumi Kanno

  2007, Proceedings of the 17th Workshop on General Relativity and Gravitation in Japan, JGRG 2007, 208 - 211, English

  International conference proceedings


• Kaluza-Klein braneworld cosmology with static internal dimensions

  S. Kanno, D. Langlois, M. Sasaki, J. Soda

  We investigate the Kaluza-Klein braneworld cosmology from the point of view of observers on the brane. We first generalize the Shiromizu-Maeda-Sasaki (SMS) equations to higher dimensions. As an application, we study a (4+n)-dimensional brane with n dimensions compactified on the brane, in a (5+n)-dimensional bulk. By assuming that the size of the internal space is static, that the bulk energy-momentum tensor can be ignored, we determine the effect of the bulk geometry on the Kaluza-Klein braneworld. Then we derive the effective Friedmann equation on the brane. It turns out that the Friedmann equation explicitly depends on the equation of state, in contrast to the braneworld in a 5-dimensional bulk spacetime. In particular, in a radiation-dominated era, the effective Newton constant depends logarithmically on the scale factor. If we include a pressureless matter on the brane, this dependence disappears after the radiation-matter equality. This may be interpreted as stabilization of the Newton constant by the matter on the brane. Our findings imply that the Kaluza-Klein braneworld cosmology is quite different from the conventional Kaluza-Klein cosmology even at low energy.

  Published for the Yukawa Institute for Theoretical Physics and the Physical Society of Japan, 2007, Progress of Theoretical Physics, 118(4) (4), 701 - 713, English

  [Refereed]


• More on the Spectrum of Perturbations in String Gas Cosmology

  Robert H. Brandenberger, Sugumi Kanno, Jiro Soda, Damien A. Easson, Justin Khoury, Patrick Martineau, Ali Nayeri, Subodh Patil

  String gas cosmology is rewritten in the Einstein frame. In an effective theory in which a gas of closed strings is coupled to a dilaton gravity background without any potential for the dilaton, the Hagedorn phase which is quasi-static in the string frame corresponds to an expanding, non-accelerating phase from the point of view of the Einstein frame. The Einstein frame curvature singularity which appears in this toy model is related to the blowing up of the dilaton in the string frame. However, for large values of the dilaton, the toy model clearly is inapplicable. Thus, there must be a new string phase which is likely to be static with frozen dilaton. With such a phase, the horizon problem can be successfully addressed in string gas cosmology. The generation of cosmological perturbations in the Hagedorn phase seeded by a gas of long strings in thermal equilibrium is reconsidered, both from the point of view of the string frame (in which it is easier to understand the generation of fluctuations) and the Einstein frame (in which the evolution equations are well known). It is shown that fixing the dilaton at some early stage is important in order to obtain a scale-invariant spectrum of cosmological fluctuations in string gas cosmology.

  Aug. 2006

  [Refereed]


• Hawking radiation from Rotating black holes and gravitational anomalies

  Keiju Murata, Jiro Soda

  Aug. 2006, PHYSICAL REVIEW D, 74(4) (4), English

  [Refereed]

  Scientific journal


• Lorentz Violating Inflation

  Sugumi Kanno, Jiro Soda

  We explore the impact of Lorentz violation on the inflationary scenario. More precisely, we study the inflationary scenario in the scalar-vector-tensor theory where the vector is constrained to be unit and time like. It turns out that the Lorentz violating vector affects the dynamics of the chaotic inflationary model and divides the inflationary stage into two parts; the Lorentz violating stage and the standard slow roll stage. We show that the universe is expanding as an exact de Sitter spacetime in the Lorentz violating stage although the inflaton field is rolling down the potential. Much more interestingly, we find exact Lorentz violating inflationary solutions in the absence of the inflaton potential. In this case, the inflation is completely associated with the Lorentz violation. We also mention some consequences of Lorentz violating inflation which can be tested by observations.

  Apr. 2006

  [Refereed]


• Evaporating (2+l)-dimensional black strings

  Keiju Muratal, Jiro Soda, Sugumi Kanno

  2006, Proceedings of the 16th Workshop on General Relativity and Gravitation in Japan, JGRG 2006, 102 - 105, English

  Scientific journal


• Impact of lorentz violation on cosmology

  Jiro Soda, Sugumi Kanno

  2006, Proceedings of the 16th Workshop on General Relativity and Gravitation in Japan, JGRG 2006, 180 - 183, English

  Scientific journal


• Moduli stabilization in string gas compactification

  S Kanno, J Soda

  Nov. 2005, PHYSICAL REVIEW D, 72(10) (10), English

  [Refereed]

  Scientific journal


• Black string perturbations in RS1 model

  S Kanno, J Soda

  Sep. 2005, GENERAL RELATIVITY AND GRAVITATION, 37(9) (9), 1651 - 1662, English

  [Refereed]

  Scientific journal


• Braneworld cosmological perturbation theory at low energy

  J Soda, S Kanno

  Sep. 2005, GENERAL RELATIVITY AND GRAVITATION, 37(9) (9), 1621 - 1628, English

  [Refereed]

  Scientific journal


• Braneworld flux inflation

  S Kanno, J Soda, D Wands

  Aug. 2005, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, (8) (8), English

  [Refereed]

  Scientific journal


• Validity of a factorizable metric ansatz in string cosmology

  S Kanno, J Soda

  Feb. 2005, PHYSICAL REVIEW D, 71(4) (4), English

  [Refereed]

  Scientific journal


• Effective action approach to string gas compactification

  Sugumi Kanno, Jiro Soda

  2005, Proceedings of the 15th Workshop on General Relativity and Gravitation in Japan, JGRG 2005, 201 - 204, English

  International conference proceedings


• A quasi-thick codimension 2 braneworld

  S Kanno, J Soda

  Jul. 2004, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, (7) (7), English

  [Refereed]

  Scientific journal


• Braneworld Kaluza-Klein corrections in a nutshell

  S Kanno, J Soda

  May 2004, PHYSICS LETTERS B, 588(3-4) (3-4), 203 - 209, English

  [Refereed]

  Scientific journal


• Low energy effective action for dilatonic braneworld - A formalism for inflationary braneworld

  S Kanno, J Soda

  Apr. 2004, GENERAL RELATIVITY AND GRAVITATION, 36(4) (4), 689 - 712, English

  [Refereed]

  Scientific journal


• Rotating black string and the effective Teukolsky equation in the braneworld

  S Kanno, J Soda

  Apr. 2004, CLASSICAL AND QUANTUM GRAVITY, 21(7) (7), 1915 - 1923, English

  [Refereed]

  Scientific journal


• Radionic Non-uniform Black Strings --short version--

  Takashi Tamaki, Sugumi Kanno, Jiro Soda

  Nov. 2003, PHYSICAL REVIEW D, 69(2) (2), English


• Born-again braneworld

  S. Kanno, M. Sasaki, J. Soda

  We propose a cosmological braneworld scenario in which two branes collide and emerge as reborn branes whose tensions have signs opposite to the original tensions of the respective branes. In this scenario, gravity on each of the branes is described by a scalar-tensor-type theory in which the radion plays the role of the gravitational scalar, and the branes are assumed to be inflating. However, the whole dynamics are different from those of the usual inflation, due to the non-trivial dynamics of the radion field. Transforming the conformal frame to the Einstein frame, this born-again scenario resembles the pre-big-bang scenario. Thus, our scenario has features of both inflation and pre-big-bang scenarios. In particular, gravitational waves produced from vacuum fluctuations may have a very blue spectrum, while the inflaton field gives rise to a standard scale-invariant spectrum.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, 2003, Progress of Theoretical Physics, 109(3) (3), 357 - 369, English

  [Refereed]


• Radion and holographic brane gravity

  S Kanno, J Soda

  Oct. 2002, PHYSICAL REVIEW D, 66(8) (8), English

  [Refereed]

  Scientific journal


• Holographic View of Cosmological Perturbations

  Jiro Soda, Sugumi Kanno

  Sep. 2002, ASTROPHYSICS AND SPACE SCIENCE, 283(4) (4), 639 - 644, English


• Braneworld Effective Action at Low Energies

  Sugumi Kanno, Jiro Soda

  Sep. 2002, ASTROPHYSICS AND SPACE SCIENCE, 283(4) (4), 481 - 486, English


• Brane world effective action at low energies and AdS/CFT correspondence

  S Kanno, J Soda

  Aug. 2002, PHYSICAL REVIEW D, 66(4) (4), English

  [Refereed]

  Scientific journal


• Bulk gravitational field and cosmological perturbations on the brane

  Kazuya Koyama, Jiro Soda

  2002, Physical Review D, 65(2) (2), English

  [Refereed]

  Scientific journal


• Cosmological perturbations in the brane world - Brane view vs bulk view

  Jiro Soda, Kazuya Koyama

  Yukawa Institute for Theoretical Physics, 2002, Progress of Theoretical Physics Supplement, 148(2) (2), 136 - 144, English

  [Refereed]

  International conference proceedings


• Thick Brane Worlds and Their Stability

  Shinpei Kobayashi, Kazuya Koyama, Jiro Soda

  Jul. 2001, Physical Review D - Particles, Fields, Gravitation and Cosmology, 65(6) (6), 9, English

  [Refereed]


• Quantum fluctuations of bulk inflaton in inflationary brane world

  Shinpei Kobayashi, Kazuya Koyama, Jiro Soda

  Elsevier BV, Mar. 2001, Physics Letters B, 501(3-4) (3-4), 157 - 164

  Scientific journal


• Strongly coupled CFT in FRW universe from AdS/CFT correspondence

  Kazuya Koyama, Jiro Soda

  Institute of Physics Publishing, 2001, Journal of High Energy Physics, 5(5) (5), English

  Scientific journal


• Evolution of cosmological perturbations in the brane world

  Kazuya Koyama, Jiro Soda

  American Physical Society, Dec. 2000, Physical Review D - Particles, Fields, Gravitation and Cosmology, 62(12) (12), 1 - 14, English

  Scientific journal


• Evolution of Fluctuations during Graceful Exit in String Cosmology

  Shinsuke Kawai, Jiro Soda

  Elsevier, Mar. 1999, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 460(1-2) (1-2), 41 - 46, English


• Instability of 1-loop superstring cosmology

  Shinsuke Kawai, Masa-aki Sakagami, Jiro Soda

  Elsevier, Feb. 1998, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 437(3-4) (3-4), 284 - 290, English


• Wavelet analysis of one-dimensional cosmological density fluctuations

  Y Fujiwara, J Soda

  Jun. 1996, PROGRESS OF THEORETICAL PHYSICS, 95(6) (6), 1059 - 1077, English

  [Refereed]

  Scientific journal


• Higher Dimensional Self-similar Spherical Symmetric Scalar Field Collapse and Critical Phenomena in Black Hole Formation

  Jiro Soda, Kouichirou Hirata

  May 1996, PHYSICS LETTERS B, 387(2) (2), 271 - 277, English


• Comment on Entropy in Two-dimensional Dilaton Gravity

  Kouichirou Hirata, Yoshi Fujiwara, Jiro Soda

  Feb. 1996, PHYSICS LETTERS B, 378(1-4) (1-4), 68 - 77, English


• Nonlinear Self-Modulation in Newtonian Gravity

  Yoshi FUJIWARA, Jiro SODA, Yukawa Institute for Theoretical Physics Kyoto Unicersity, Department of Fundamental Sciendes FIHS Kyoto University

  We study quasi-nonlinear of the density perturbation in Newtonian gravity. Weak mode-mode coupling in a small range below the Jeans wavelength is considered. In order to extract nonlinear dynamics we utilize a reductive perturbation. We show that the basic equations for the acoustic wave reduce to a nonlinear Schrodinger equation. It describes a compempetition between dispersion originated from gravitational attraction and nonlinearity up to cubic order of the amplitudeof the acoustic wave. In purely 1-dimensional motion, there exists localized structures as soliton solutions of two distinctive types depending on the wavelength. More interesting is an instability present in 3-dimensional motion. Namely, a progressive wave is unstable under a long-wave perturbation transverse to the direction of progression. It may imply a possible nonlinear growth of the density fluctuation below the Jeans scale.

  THE PHYSICAL SOCIETY OF JAPAN, Jan. 1996, Progress of theoretical physics = Progress of theoretical physics, 95(1) (1), 51 - 63, English


• A possible way of stabilizing a higher-dimensional universe

  Y. Ezawa, J. Soda, T. Watanabe, T. Yano

  Editrice Compositori s.r.l., 1996, Nuovo Cimento della Societa Italiana di Fisica B, 111(3) (3), 355 - 362, English

  Scientific journal


• A HIDDEN SYMMETRY IN THE ONE-DIMENSIONAL COSMOLOGICAL MODEL

  J SODA

  Sep. 1993, PROGRESS OF THEORETICAL PHYSICS, 90(3) (3), 569 - 575, English

  [Refereed]

  Scientific journal


• Hierarchical Dimensional Reduction and Gluing Geometries : Particles and Fields

  Jiro SODA, Department of Physics Faculty of General Education Ehime University

  The various 2-dimensional models of gravity are deduced from the hierarchical dimensional reduction. They include the infinite dimensional Schwarzschild black hole which is studied by Callan et al. The various new geometries are constructed by gluing them. In particular, the possibility of dimension change is pointed out.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, Jun. 1993, Progress of theoretical physics = Progress of theoretical physics, 89(6) (6), 1303 - 1310, English


• Axially symmetric domain wall in 2 + 1 dimensions

  Jiro Soda, Yuki Yamanaka

  Oct. 1991, Physics Letters B, 269(3-4) (3-4), 275 - 278, English

  Scientific journal


• Junction Conditions in 2+1-Dimensional Gravity : Astrophysics and Relativity

  Jiro SODA, Yuki YAMANAKA, Hiroo OOGUCHI, Uji Research Center Yukawa Institute for Theoretical Physics Kyoto University, Uji Research Center Yukawa Institute for Theoretical Physics Kyoto University, Uji Research Center Yukawa Institute for Theoretical Physics Kyoto University

  Possible junctions among Minkowski, Cone and de Sitter space-times are exhausted. Using the positive energy condition for the string, the possible space-times are restricted. The motions of the string in various cases are solved.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, Oct. 1991, Progress of theoretical physics = Progress of theoretical physics, 86(4) (4), 841 - 852, English


• How Many ``Times'' Do We Have In Quantum Gravity? : A Path-Integral Approach : Astrophysics and Relativity

  Akio HOSOYA, jiro SODA, Department of Physics Tokyo Institute of Technology, Department of Physics Hiroshima University:Uji Research Center Yukawa Institute for Theoretical Physics Kyoto University

  Apparently there are an infinite number of time-like variables in the Wheeler-DeWitt equation in quantum gravity.This gives rise to an obvious conceptual difficulty and further becomes an obstacle if one wants to canonically third quantize the universe. In this paper, adopting York's gauge in the path-integral approach, we formulate quantum geometrodynamics so that it contains only a single time-like variable corresponding to the total volume of the universe.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, Dec. 1990, Progress of theoretical physics = Progress of theoretical physics, 84(6) (6), 1108 - 1114, English


• Linearized Analysis of (2+1)-Dimensional Einstein-Maxwell Theory : Particles and Fields

  Jiro SODA, Research Institute for Theoretical Physics Hiroshima University

  On the basis of previous result by Hosoya and Nakao that (2+1)-dimensional gravity reduces the geodesic motion in moduli space, we investigate the effects of matter fields on the geodesic motion using the linearized theory. It is shown that the transverse-traceless parts of energy-momentum tensor make the deviation from the geodesic motion. This result is important for the Einstein-Maxwell theory due to the existence of global modes of Maxwell fields on torus.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, Apr. 1990, Progress of theoretical physics = Progress of theoretical physics, 83(4) (4), 805 - 813, English


• Teichmuller Motion of (2+1)-Dimensional Gravity with the Cosmological Constant : Astrophysics and Relativity

  Yoshihisa FUJIWARA, Jiro SODA, Research Institute for Theoretical Physics Hiroshima University, Research Institute for Theoretical Physics Hiroshima University

  The (2+1)-dimensional Einstein gravity with a cosmological constant is studied in the ADM canonical formalism. Adopting York's time slice, we completely solve the initial-value problem and the time evolution equations with an initial spacelike 2-surface being a closed Riemann surface of genus zero and one. The result in a torus case is that the Teichmuller parameters for the torus follow a geodesic in the Teichmuller space but its motion asymptotically stops due to the presence of the cosmological constant.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, Apr. 1990, Progress of theoretical physics = Progress of theoretical physics, 83(4) (4), 733 - 748, English


• Reducing the Huge Symmetry Occurring in the Compactification of a String

  Jiro SODA, Research Institute for Theoretical Physics Hiroshima University

  For the problem of the huge symmetry which occurs after the compactification, we propose a mechanism of reducing the symmetry. The realistic symmetry is obtained by introducing the para-quantization, whose number and order are determined by the masslessness of graviton. We also discuss the interpretation of our formulation.

  Published for the Research Institute for Fundamental Physics by Physical Society of Japan, May 1988, Progress of theoretical physics = Progress of theoretical physics, 79(5) (5), 1016 - 1021, English

• Impact of quantum entanglement induced by magnetic fields on primordial gravitational waves

  Sugumi Kanno, Ann Nakato, Jiro Soda, Kazushige Ueda

  There exist observational evidence to believe the existence of primordial magnetic fields generated during inflation. We study primordial gravitational waves (PGWs) during inflation in the presence of magnetic fields sustained by a gauge kinetic coupling. In the model, not only gravitons as excitations of PGWs, but also photons as excitations of electromagnetic fields are highly squeezed. They become entangled with each other through graviton to photon conversion and vice versa. We derive the reduced density matrix for the gravitons and calculate their entanglement entropy. It turns out that the state of the gravitons is not a squeezed state but a mixed state.

  10 Nov. 2022

  Link to Kobe Univ. Repository (Kernel)


• Anisotropic warm inflation

  Sugumi Kanno, Ann Nakato, Jiro Soda, Kazushige Ueda

  Anisotropic inflation is a model succeeded in explaining statistical anisotropy. Warm inflation is a model succeeded in providing a mechanism of reheating during inflation. We study anisotropic warm inflation focusing on the cosmic no-hair conjecture. In the anisotropic warm inflation, the condition for making anisotropy survived is clarified. We find exact solutions of power-law anisotropic warm inflation, and investigate the phase space structure of general solutions. It turns out that whether the anisotropy during inflation survives or not depends on the speed of decaying process from inflaton field into matter fields. If the process is very slow, the anisotropic warm inflation is realized. If the process is slow, the anisotropy tends to be hard to grow enough in the duration of inflation. If the process is rapid, no anisotropic inflation occurs.

  13 Sep. 2022

  Link to Kobe Univ. Repository (Kernel)


• 22pSN-5 Anisotropic non-Gaussianity from a two-form field

  Ohashi Junko, Soda Jiro, Tsujikawa Shinji

  The Physical Society of Japan (JPS), 26 Aug. 2013, Meeting abstracts of the Physical Society of Japan, 68(2) (2), 114 - 114, Japanese


• 空間・時間・物質と次元 : 相対論から高次元時空へ (特集 次元の作法 : 物理を表現する心得)

  早田 次郎

  サイエンス社, May 2013, 数理科学, 51(5) (5), 28 - 33, Japanese


• Statistical anisotropy from anisotropic inflation

  Jiro Soda

  Apr. 2012, CLASSICAL AND QUANTUM GRAVITY, 29(8) (8), 1 - 83001, English

  Book review


• 宇宙線・宇宙物理領域・素粒子実験領域「CMBで探る初期宇宙とPhysics beyond the Standard Model」(2011年秋季大会シンポジウムの報告,学会報告)

  早田 次郎

  一般社団法人日本物理学会, 05 Feb. 2012, 日本物理學會誌, 67(2) (2), 114 - 115, Japanese


• 25pGR-1 Symmetry Breaking and Inflation

  Soda Jiro

  The Physical Society of Japan (JPS), 03 Mar. 2011, Meeting abstracts of the Physical Society of Japan, 66(1) (1), 105 - 105, Japanese


• AdS/CFT on the brane

  Jiro Soda

  2011, Lecture Notes in Physics, 828, 235 - 270, English

  Technical report


• Progress of Theoretical Physics: Preface

  Misao Sasaki, Jiro Soda, Takahiro Tanaka, Toshifumi Futamase, Hideo Kodama, Yasufumi Kojima, Kei Ichi Maeda, Shinji Mukohyama, Nobuyoshi Ohta, Ken'ichi Oohara, Masaru Shibata, Tetsuya Shiromizu, Masahiro Yamaguchi, Jun'ichi Yokoyama, Wataru Hikida, Kunihito Ioka, Noriyuki Kogo, Shigehiro Nagataki, Takashi Nakamura

  31 Oct. 2006, Progress of Theoretical Physics


• The next chapter in Einstein's legacy - Preface

  Misao Sasaki, Jiro Soda, Takahiro Tanaka

  2006, PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (163) (163), I - II, English

  Others


• 宇宙項問題とDブレーンインフレーション (特集 量子重力理論最前線--弦・ブレーン・ループが広げる新地平)

  早田 次郎, 菅野 優美

  サイエンス社, Apr. 2005, 数理科学, 43(4) (4), 20 - 25, Japanese


• On The Higher Codimension Braneworld

  Sugumi Kanno, Jiro Soda

  We study a codimension 2 braneworld in the Einstein-Gauss-Bonnet gravity. In the linear regime, we show the conventional Einstein gravity can be recovered on the brane. While, in the nonlinear regime, we find corrections due to the thickness and the bulk geometry.

  15 Oct. 2004


• Braneworld Cosmology

  Jiro Soda, Sugumi Kanno

  We present a general formalism for studying an inflationary scenario in the two-brane system. We explain the gradient expansion method and obtain the 4-dimensional effective action. Based on this effective action, we give a basic equations for the background homogeneous universe and the cosmological perturbations. As an application, we propose a born-again braneworld scenario.

  15 Oct. 2004


• ブレーンワールドの創世と進化--衝突する4次元宇宙 (特集 ブレーンワールド新展開--時空の幾何学が示す新しい物理像)

  早田 次郎, 菅野 優美

  サイエンス社, Jan. 2004, 数理科学, 42(1) (1), 26 - 32, Japanese


• A Novel Approach to Braneworld

  Jiro Soda, Sugumi Kanno

  Evaluating Kaluza-Klein (KK) corrections is indispensable to test the braneworld scenario. In this report, we propose a novel symmetry approach to an effective 4-dimensional action with KK corrections for the Randall-Sundrum two-brane system.

  24 Dec. 2003


• Effective Teukolsky Equation on the Brane

  Sugumi Kanno, Jiro Soda

  To estimate Kaluza-Klein (KK) corrections on gravitational waves emitted by perturbed rotating black strings, we give the effective Teukolsky equation on the brane which is separable equation and hence numerically manageable.

  22 Dec. 2003


• Radionic Non-uniform Stable Black Strings

  Takashi Tamaki, Sugumi Kanno, Jiro Soda

  Non-uniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a non-trivial hair of black strings. The stability of solutions is demonstrated using the catastrophe theory. The black strings are shown to be non-uniform.

  18 Dec. 2003


• Colliding Braneworlds

  Soda Jiro

  The Physical Society of Japan (JPS), 06 Mar. 2003, Meeting abstracts of the Physical Society of Japan, 58(1) (1), 87 - 87, Japanese


• 宇宙波動関数と解釈問題--量子宇宙から古典宇宙へ (特集 波動関数のミステリー 量子力学の解釈とその不思議)

  早田 次郎

  サイエンス社, Jul. 2002, 数理科学, 40(7) (7), 43 - 49, Japanese


• Gravitational Waves in Brane World -A Midi-superspace Approach-

  Jiro Soda

  It is important to reveal the brane-bulk correspondence for understanding the
  brane world cosmology. When gravitational waves exist in the bulk, however, it
  is difficult to make the analysis of the interrelationship between the brane
  and the bulk. Hence, the minimal model which allows gravitational waves in the
  bulk would be useful. As for such models, we adopt the Bianchi type
  midi-superspace models. In particular, the effects of gravitational waves in
  the bulk on the brane cosmology is examined using the midi-superspace approach.

  03 Feb. 2002

  Technical report


• Branes for Relativists

  Jiro Soda

  Recently, branes in supergravity have become an indispensable tool even for traditional relativists. The purpose of this manuscript is to provide a pedagogical account of the brane technology so that the relativists can use branes in their study. The type IIA supergravity theory is mainly discussed and other cases are briefly mentioned. The repulson singularity is also explained as an interesting application.

  18 Aug. 2001

  Technical report


• Black Hole in Higher Curvature Gravity and AdS/CFT Correspondence

  Hiromi Saida, Jiro Soda

  The classical central charge for the higher curvature gravity in 3-dimensions is calculated using the Legendre transformation method. The statistical entropy of BTZ black hole is derived by the Cardy's formula and the result completely coincides with the Iyer-Wald formula for the geometrical entropy. This coincidence suggests the generalized AdS/CFT correspondence.

  27 Nov. 2000


• BTZ Black Hole Entropy in Higher Curvature Gravity

  Hiromi Saida, Jiro Soda

  For the BTZ black hole in the Einstein gravity, a statistical entropy has been calculated. It is equal to the Bekenstein-Hawking entropy. In this article, its statistical entropy in the higer curvature gravity is calculated and shown to be equal to one derived by using the Noether charge method. This suggests that the equivalence between the geometrical and statistical entropies of the black hole is retained in the general diffeomorphism invariant theories of gravity. A relation between the cosmic censorship conjecture and the unitarity of the conformal field theory on the boundary of AdS_3 is also discussed.

  07 Jan. 2000, Phys.Lett. B471 (2000) 358-366, 471(4) (4), 358 - 366

  Technical report


• Black holes and a scalar field in an expanding universe

  Hiromi Saida, Jiro Soda

  2000, Classical and Quantum Gravity, 17(24) (24), 4967 - 4980


• Statistical entropy of BTZ black hole in higher curvature gravity

  H Saida, J Soda

  Jan. 2000, PHYSICS LETTERS B, 471(4) (4), 358 - 366, English

  Technical report


• Structure Formation in Non-singular Higher Curvature Cosmology

  Shinsuke Kawai, Jiro Soda

  We propose novel structure formation scenarios based on a non-singular higher
  curvature cosmological model. The model is motivated by the $R^2$ coupling of a
  scalar field appearing in the string theory, and in our scenarios the universe
  has no beginning and no end. We give two examples with explicit parameter
  values which are consistent with present observations of the cosmological
  structure. In the first example, the origin of structures are generated as the
  adiabatic perturbation during the chaotic inflation, while in the second the
  isocurvature non-Gaussian perturbation from the superinf...

  15 Jun. 1999

  Technical report


• Perturbative analysis of non-singular cosmological model

  Shinsuke Kawai, Masa-aki Sakagami, Jiro Soda

  A stability analysis is made for a non-singular pre-big-bang like cosmological model based on 1-loop corrected string effective action. Its homogeneous and isotropic solution realizes non-singular transition from de Sitter universe to Friedmann-like universe, via super inflation phase. We are interested in whether the non-singular nature of the solution would be stable or not in more general inhomogeneous case. Perturbative analysis is made for scalar, vector, and tensor linear perturbations, and instability is found for tensor-type perturbation.

  23 Jan. 1999


• Nonsingular Bianchi type I cosmological solutions from the 1-loop superstring effective action

  Shinsuke Kawai

  1999, Physical Review D - Particles, Fields, Gravitation and Cosmology, 59(6) (6), English

  Technical report


• Baryon Isocurvature Perturbation in the Affleck-Dine Baryogenesis mechanism

  Kazuya Koyama, Jiro Soda

  01 Oct. 1998, Physical Review Letters, 82(13) (13), 2632 - 2635, English

  Technical report


• On the Canonical Formalism for a Higher-Curvature Gravity

  Yasuo Ezawa, Masahiko Kiminami, Masahiro Kajihara, Jiro Soda, Tadasi Yano

  Following the method of Buchbinder and Lyahovich, we carry out a canonical formalism for a higher-curvature gravity in which the Lagrangian density ${\cal L}$ is given in terms of a function of the salar curvature $R$ as ${\cal L}=\sqrt{-\det g_{\mu\nu } }f(R)$. The local Hamiltonian is obtained by a canonical transformation which interchanges a pair of the generalized coordinate and its canonical momentum coming from the higher derivative of the metric.

  26 Jan. 1998


• Inhomogeneity of spatial curvature for inflation

  O Iguchi, H Ishihara, J Soda

  Mar. 1997, PHYSICAL REVIEW D, 55(6) (6), 3337 - 3345, English


• Critical Behavior in the Brans-Dicke Theory of Gravitation

  Takeshi Chiba, Jiro Soda

  Yukawa Institute for Theoretical Physics, 28 Mar. 1996, Progress of Theoretical Physics, 96(3) (3), 567 - 574, English

  Technical report


• Hamilton-Jacobi Equation for Brans-Dicke Theory and Its Long-wavelength Solution

  Jiro Soda, Hideki Ishihara, Osamu Iguchi

  Hamilton-Jacobi equation for Brans-Dicke theory is solved by using a long-wavelength approximation. We examine the non-linear evolution of the inhomogeneities in the dust fluid case and the cosmological constant case. In the case of dust fluid, it turns out that the inhomogeneities of space-time grow. In the case of cosmological constant, the inhomogeneities decay, which is consistent with the cosmic no hair conjecture. The inhomogeneities of the density perturbation and the gravitational constant behave similarly with that of space-time.

  THE PHYSICAL SOCIETY OF JAPAN, 06 Sep. 1995, Progress of theoretical physics = Progress of theoretical physics, 94(5) (5), 781 - 793, English


• 3-dimensional Gravity and Regge Calculus

  SODA Jiro

  Soryushiron Kenkyu, 20 Dec. 1991, Soryushiron Kenkyu, 84(3) (3), C36 - C42, English


• KAC FORMULAS FOR G/H CONFORMAL FIELD-THEORIES

  J SODA, H YOSHII

  Dec. 1988, PROGRESS OF THEORETICAL PHYSICS, 80(6) (6), 941 - 946, English

  Report scientific journal

• 臨時別冊数理科学 SGCライブラリ 46 「現代物理のための解析力学」 2006年 03月号

  早田次郎

  Single work, サイエンス社, 2006


• 現代物理のための解析力学

  早田 次郎

  サイエンス社, 2006, Japanese


• 宇宙背景輻射による余剰次元の観測

  早田 次郎, 京都大学大学院理学研究科

  [早田次郎], 2006, English


• The Next Chapter in Einstein's Legacy : proceedings of the Yukawa International Seminar 2005 : (YKIS 2005) : Yukawa Institute for Theoretical Physics, Kyoto University, 27 June - 1 July, 2005

  Yukawa International, Symposium, 佐々木 節, 早田 次郎, 田中 貴浩

  Progress of Theoretical Physics, 2006, English


• 現代物理を学ぶための理論物理学

  C.F. スティーブンス

  Single translation, 吉岡書店, Oct. 1997, Japanese, ISBN: 4842702672

• 磁場とアクシオン暗黒物質が共存する系における光子の伝播

  MASAKI Emi, AOKI Arata, JIRO Soda

  日本物理学会第74回年次大会, Mar. 2019, Japanese, 日本物理学会, 九州大学, Domestic conference

  Oral presentation


• マグノンを用いたアクシオンダークマター探索

  TSUNETO Makoto, ITO Asuka, NOUMI Toshifumi, JIRO Soda

  日本物理学会第74回年次大会, Mar. 2019, Japanese, 日本物理学会, 九州大学, Domestic conference

  Oral presentation


• ブラックホール上の微分形式場

  YOSHIDA Daisuke, JIRO Soda

  日本物理学会, Mar. 2019, Japanese, 日本物理学会, 九州大学, Domestic conference

  Oral presentation


• パルサータイミングアレイによるアクシオンダークマター分析

  KATO Ryo, JIRO Soda

  日本物理学会, Mar. 2019, Japanese, 日本物理学会, 九州大学, Domestic conference

  Oral presentation


• 物理学は宇宙大規模構造の起源を明らかにできるのか

  JIRO Soda

  理論懇シンポジウム, Feb. 2019, Japanese, 京都大学基礎物理学研究所, Domestic conference

  [Invited]

  Invited oral presentation


• Parity Violation in Gravity: probing with gravitational waves

  JIRO Soda

  新学術「重力波物理学」, Feb. 2019, English, 長岡科学技術大学, Domestic conference

  [Invited]

  Invited oral presentation


• Searching for the axion dark matter with pulsar timing arrays

  KATO Ryo, JIRO Soda

  国際会議「The 28th Workshop on General Relativity and Gravitation in Japan」, Dec. 2018, English, 京都大学, International conference

  Oral presentation


• String axions in the Sky

  JIRO Soda

  セミナー, Nov. 2018, Japanese, 立教大学, Domestic conference

  Public discourse


• Primordial Gravitational Waves

  JIRO Soda

  国際会議「String Axion Cosmology」, Nov. 2018, English, SKKU, 韓国, International conference

  [Invited]

  Invited oral presentation


• Nonclassicality of Primordial Gravitational Waves

  JIRO Soda

  新学術国際会議, Nov. 2018, English, 京都大学基礎物理学研究所, International conference

  [Invited]

  Invited oral presentation


• Detectability of gravitons with HBT interfereometers

  早田 次郎

  String axion cosmology, Nov. 2018, English, 成均館大学校, International conference

  [Invited]

  Invited oral presentation


• Axion-Photon Conversion in the Presence of Oscillating Axion Background” The 28th Workshop on General Relativity and Gravitation in Japan, Tachikawa Memori

  MASAKI Emi, AOKI Arata, JIRO Soda

  The 28th Workshop on General Relativity and Gravitation in Japan, Nov. 2018, English, 立教大学, International conference

  Oral presentation


• A strategy for detecting the bispectrum of stochastic gravitational waves.

  TSUNETO Makoto, ITO Asuka, NOUMI Toshifumi, JIRO Soda

  The 28th Workshop on General Relativity and Gravitation in Japan, Nov. 2018, English, 立教大学, Domestic conference

  Oral presentation


• 背景重力波のバイスペクトル観測

  TSUNETO Makoto, ITO Asuka, NOUMI Toshifumi, JIRO Soda

  日本物理学会 2018年度秋季大会, Sep. 2018, Japanese, 日本物理学会, 信州大学, Domestic conference

  Oral presentation


• パルサータイミングアレイによるアクシオンダークマター探索

  KATO Ryo, JIRO Soda

  日本物理学会 2018年度秋季大会, Sep. 2018, Japanese, 日本物理学会, 信州大学, Domestic conference

  Oral presentation


• パルサータイミングアレイによるアクシオンダークマターへの制限

  KATO Ryo, SODA Jiro

  日本物理学会, Sep. 2018, Japanese, 日本物理学会, 宇都宮大学, Domestic conference

  Oral presentation


• アクシオン暗黒物質を背景とする光子・アクシオン転換

  MASAKI Emi, AOKI Arata, JIRO Soda

  日本物理学会 2018年度秋季大会, Sep. 2018, Japanese, 日本物理学会, 信州大学, Domestic conference

  Oral presentation


• String axions, flapping resonance, and GW forest

  JIRO Soda

  国際会議「5th Korean-Japan Workshop on Dark Energy: Starobinsky’s Universe」, Aug. 2018, English, KASI(韓国）, International conference

  [Invited]

  Invited oral presentation


• GW forest from the string axiverse

  SODA Jiro

  5th Korea-Japan Workshop on Dark Energy, Aug. 2018, English, Korea Astronomy and Space Science Institute, Starobinsky's Universe, International conference

  [Invited]

  Invited oral presentation


• GW forest from the string axiverse

  NAOYA Kitajima, SODA Jiro, URAKAWA Yoko

  SUSY 2018, Jul. 2018, English, SUSY, Barcelona, International conference

  Oral presentation


• Gravitational waves forest from string axiverse

  JIRO Soda

  SUSY2018, Jul. 2018, English, バルセロナ, International conference

  Oral presentation


• Glaubers in the Sky

  JIRO Soda

  国際会議「The first NRF-JSPS workshop in particle physics, cosmology, and gravity」, Jul. 2018, English, 支笏湖, International conference

  [Invited]

  Invited oral presentation


• Glauber in the sky

  SODA Jiro

  The first NRF-JSPS workshop in particle physics,cosmology, and gravitation, Jul. 2018, English, NRF-JSPS, 北海道, International conference

  [Invited]

  Invited oral presentation


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  YOSHIDA Daisuke, JIRO Soda

  15th Marcel Grossmann Meeting - MG15, Jul. 2018, English, University of Rome "La Sapienza, Rome, Italy, International conference

  Oral presentation


• A strategy for detecting the bispectrum of stochastic gravitational waves.

  TSUNETO Makoto, ITO Asuka, NOUMI Toshifumi, JIRO Soda

  15th Marcel Grossmann meeting, Jul. 2018, English, Roma, Italy, International conference

  Oral presentation


• 原始重力波の量子コヒーレンス

  JIRO Soda

  研究会「量子情報と宇宙」, Jun. 2018, Japanese, KobeUniversity, KobeUniversity, Domestic conference

  Public discourse


• Cosmological Bell Inequality and Entangled Quantum Vacuum

  SODA Jiro

  International workshop for String theory, Gravitation and Cosmology (STGCOS) 2018’, Jun. 2018, English, STGCOS, Korea, International conference

  [Invited]

  Invited oral presentation


• Cosmological Bell Inequality and entangled quantum Vacuum

  JIRO Soda

  国際会議「International workshop for string theory and cosmology」、APCTP, Jun. 2018, English, 韓国, International conference

  [Invited]

  Invited oral presentation


• Constraint on the axion dark matter using pulsar timing arrays

  KATO Ryo, JIRO Soda

  国際会議「2018 International Pulsar Timing Array conference」, Jun. 2018, English, アルバカーキ, International conference

  Oral presentation


• 原始重力波の量子コヒーレンス

  SODA Jiro

  日本物理学会, Mar. 2018, Japanese, 日本物理学会, 東京理科大, Domestic conference

  Oral presentation


• String Axions in the Sky

  SODA Jiro

  重力・宇宙研究会, Mar. 2018, Japanese, 山口大学, 山口大学, Domestic conference

  [Invited]

  Nominated symposium


• Anisotropic constant-roll inflation

  ITO Asuka, SODA Jiro

  日本物理学会, Mar. 2018, Japanese, 日本物理学会, 宮崎大学, Domestic conference

  Oral presentation


• パルサータイミングアレイによるアクシオンダークマター解析

  KATO Ryo, SODA Jiro

  日本物理学会, Feb. 2018, Japanese, 日本物理学会, 東京理科大学, Domestic conference

  Oral presentation


• String axions in Chern-Simons gravity

  SODA Jiro

  加速宇宙シンポジウム, Feb. 2018, English, 東北大学, 東北大学, Domestic conference

  [Invited]

  Nominated symposium


• Primordial gravitational waves and early universes

  ITO Asuka, SODA Jiro

  YIKIS2018a Symposium, Feb. 2018, English, YIKIS, 京都, International conference

  Poster presentation


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  吉田 大祐, SODA Jiro

  国際会議「YKIS2018a Symposium General Relativity - The Next Generation -」, Feb. 2018, English, YKIS, 基礎物理学研究所, International conference

  Poster presentation


• Electromagnetic waves propagating in the string axiverse

  吉田 大祐, SODA Jiro

  日本物理学会, Feb. 2018, Japanese, 日本物理学会, 東京理科大学, Domestic conference

  Oral presentation


• Constraint on the axion dark matter using pulsar timing arrays

  KATO Ryo, SODA Jiro

  国際会議「YKIS2018a Symposium General Relativity - The Next Generation -」, Feb. 2018, English, YKIS, 京都大学, International conference

  Public symposium


• Axion-Photon Conversion in the Presence of Oscillating Axion Background

  MASAKI Emi, AOKI Arata, JIRO Soda

  Korea-Japan bilateral workshop on String axion cosmology, 2018, English, Sungkyunkwan Universityty, Korea, International conference

  [Invited]

  Invited oral presentation


• インフレーション中の揺らぎの量子相関

  SODA Jiro

  集中講義, Jan. 2018, Japanese, 名古屋大学, 名古屋大学, Domestic conference

  Public discourse


• String moduli, string axiverse, and gravitational waves

  SODA Jiro

  国際会議「7th Bangkok Workshop on High-Energy Theory」, Jan. 2018, English, タイ, International conference

  Oral presentation


• Gravitational waves in the string axiverse

  SODA Jiro

  国際会議「NCTS Annual meeting 2017」, Dec. 2017, English, 国立清華大学, 台湾, International conference

  [Invited]

  Invited oral presentation


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  吉田 大祐, SODA Jiro

  国際会議「International Symposium on Cosmology and Particle Astrophysics CosPA 2017」, Dec. 2017, English, 基礎物理学研究所, 京都大学, International conference

  Public symposium


• Constraint on the axion dark matter using pulsar timing arrays

  KATO Ryo, SODA Jiro

  国際会議「International Symposium on Cosmology and Particle Astrophysics (CosPA 2017)」, Dec. 2017, English, CosPA, 京都大学, International conference

  Oral presentation


• Primordial gravitational waves and early universes

  ITO Asuka, SODA Jiro

  CosPA (International Symposium on Cosmology and Particle Astrophysics), Nov. 2017, English, 広島, International conference

  Public symposium


• Exploring the string axiverse and parity violation in gravity with gravitational waves

  吉田 大祐, SODA Jiro

  国際会議「The 27th Workshop on General Relativity and Gravitation in Japan」, Nov. 2017, English, 広島, International conference

  Public symposium


• Constraint on the axion dark matter using pulsar timing arrays

  KATO Ryo, SODA Jiro

  国際会議「The 28th Workshop on General Relativity and Gravitation in Japan」, Nov. 2017, English, 広島, International conference

  Oral presentation


• 超軽量アクシオン暗黒物質による構造形成

  AOKI Arata, SODA Jiro

  日本物理学会 2017年秋季大会, Sep. 2017, Japanese, 日本物理学会, 宇都宮大学, Domestic conference

  Oral presentation


• Infinite violation of Bell inequalities

  SODA Jiro

  日本物理学会, Sep. 2017, Japanese, 日本物理学会, 宇都宮大学, Domestic conference

  Oral presentation


• Dynamical Chern-Simons gravityにおけるスカラー場振動による重力波共鳴

  吉田 大祐, SODA Jiro

  日本物理学会, Sep. 2017, English, 日本物理学会, 宇都宮大学, Domestic conference

  Oral presentation


• ベルの不等式関連の話

  SODA Jiro

  研究会「曲がった時空上の場の量子論と量子情報, Jun. 2017, Japanese, 広島大学, 広島大学, Domestic conference

  Public discourse


• Exploring string axiverse with gravitational wave physics

  SODA Jiro

  国際会議「IV Cosmology and the Quantum Vacuum 2017」, Jun. 2017, English, スペイン, International conference

  [Invited]

  Invited oral presentation


• Infinite violation of Bell inequalities

  SODA Jiro

  NCTSセミナー, May 2017, English, 国立清華大学, 台湾, International conference

  Public discourse


• 連続磁場中での Axion-Photon Conversion が与える偏光への効果

  正木 愛美, 青木 新, 早田 次郎

  日本物理学会 第 72 回年次大会, Mar. 2017, Japanese, 大阪大学, 大阪大学, Domestic conference

  Oral presentation


• Ultralight axion dark matter in accelerating universe

  早田 次郎

  新学術「加速宇宙」シ ンポジウム, Mar. 2017, English, KEK, Domestic conference

  [Invited]

  Invited oral presentation


• f(R)理論におけるアクシオン・スカラロン共鳴

  青木 新, 早田 次郎

  日本物理学会第 72 回 年次大会, Mar. 2017, Japanese, 大阪大学, 大阪大学, Domestic conference

  Oral presentation


• CMB Anomaly and Inflation with Spontaneous Symmetry Breakdown

  早田 次郎

  国際 会議「Physics in LHC and the Early Universe」, Jan. 2017, English, 東京大学, 東京大学, International conference

  [Invited]

  Invited oral presentation


• 宇宙観測における異常性から探る基礎物理学

  早田 次郎

  第５回観測的宇宙論研究会, Nov. 2016, Japanese, 広島大学, 広島大学, Domestic conference

  Public discourse


• Radiation memory of Axion-electrodynamics

  Daiske Yoshida, SODA Jiro

  The 26th Workshop on General Relativity and Gravitation in Japan, Oct. 2016, English, 大阪市立大学, Osaka City University, International conference

  Oral presentation


• Probing ultralight scalar dark matter with pulsar timing arrays

  加藤 亮, 早田 次郎

  The 26th Workshop on General Relativity and Gravitation in Japan, Osaka City U., Oct. 2016, English, 大阪市立大学, International conference

  Oral presentation


• Effects of ALP-Photon Conversion on Gamma-ray Bursts Polarization

  Emi Masaki, Arata Aoki, SODA Jiro

  The 26th Workshop on General Relativity and Gravitation in Japan, Oct. 2016, English, ISGRS, 大阪, International conference

  Poster presentation


• 修正重力理論におけるアクシオン暗黒物質の検出可能性

  青木 新, 早田 次郎

  日本物理 学会 2016 年秋季大会, Sep. 2016, Japanese, 宮崎大学, Domestic conference

  Oral presentation


• パルサータイミングアレイによるアクシオンダークマターの観測可能性

  加藤 亮, 早田 次郎

  日本物理学会 2016 年秋季大会, Sep. 2016, Japanese, 宮崎大学, 宮崎大学, Domestic conference

  Oral presentation


• Quantum discord in the multiverse

  早田 次郎

  日本物理学会, Sep. 2016, Japanese, 宮崎大学, 宮崎大学, Domestic conference

  Oral presentation


• Probing Quantum Correlation in de Sitter Universe

  早田 次郎

  国際会議「Varying Constants and Fundamental Cosmology」, Sep. 2016, English, Maritime 大学, ポーランド、シュチェチン, International conference

  [Invited]

  Invited oral presentation


• Probing Ultralight AxionDark Matter

  早田 次郎

  国際会議「International workshop for string theory and cosmology」, Aug. 2016, English, 韓国, International conference

  [Invited]

  Invited oral presentation


• Gauge Fields, Statistical Anisotropy, and Anisotropic Inflation

  早田 次郎

  素粒子セミナ ー, Jun. 2016, English, 大阪大学, 大阪大学, Domestic conference

  Public discourse


• 宇宙論的揺らぎの量子性について

  早田次郎

  日本物理学会, Mar. 2016, Japanese, 東北学院大学, 仙台, Domestic conference

  Oral presentation


• Axion 電磁気学における radiation memory

  加藤 亮, 早田 次郎, 友田 健太郎

  日本物理学会, 2016, Japanese, 宮崎大学, 宮崎大学, Domestic conference

  Oral presentation


• 素粒子的宇宙物理学B

  早田次郎

  集中講義, Jan. 2016, Japanese, 早稲田大学, 東京, Domestic conference

  Public discourse


• Physics with Pulsar Timing Arrays

  早田次郎

  招待セミナー, Jan. 2016, English, 早稲田大学, 東京, Domestic conference

  Public discourse


• ゲージ場が生み出す時空の微細構造

  早田次郎

  テラスケール研究会2015, Dec. 2015, Japanese, 東京工業大学, 東京, Domestic conference

  Public discourse


• Anisotropic Inflation and CMB

  早田次郎

  招待セミナー, Sep. 2015, English, バスク大学, スペイン, International conference

  Public discourse


• Designing Anisotropic Inflation

  早田次郎

  International Workshop for String Theory and Cosmology, Jun. 2015, English, 釜山, International conference

  [Invited]

  Invited oral presentation


• Anisotropic Inflation and CMB

  早田次郎

  中国物理学会, Jun. 2015, English, 杭州（中国）, International conference

  [Invited]

  Invited oral presentation


• 非等方インフレーション

  早田次郎

  集中講義, Apr. 2015, Japanese, 名古屋大学, 名古屋大学, Domestic conference

  [Invited]

  Invited oral presentation


• Statistical Anisotropy in the CMB from a two-form field

  早田次郎

  KMIセミナー, Apr. 2015, Japanese, 名古屋大学, 名古屋大学, Domestic conference

  [Invited]

  Invited oral presentation


• Quantum Negativity in de Sitter Space

  早田 次郎

  日本物理学会 2015年春季大会, Mar. 2015, Japanese, 早稲田大学, Domestic conference

  Oral presentation


• Impact of Form Fields on Primordial Gravitationa

  早田 次郎

  B-mode Cosmology, Feb. 2015, English, KEK, International conference

  [Invited]

  Invited oral presentation


• 膨張宇宙でのSchwinger効果

  早田 次郎

  日本物理学会 2014年秋季大会, Sep. 2014, Japanese, 佐賀大学, Domestic conference

  Oral presentation


• Anisotropic powe-law inflation

  早田 次郎

  The Spanish Relativity Meeting 2014 (ERE2014), Sep. 2014, English, バレンシア大学,Spain, International conference

  Oral presentation


• A class of superintegrable systems in E3 and its Eisenhart spacetime

  宝利 剛, 早田 次郎, 山本 慧

  日本物理学会 2014年秋季大会, Sep. 2014, English, 佐賀大学, Domestic conference

  Poster presentation


• Quantum Entanglement in de Sitter Space

  早田 次郎

  名古屋大学招待セミナー, Jul. 2014, Japanese, 名古屋大学, Domestic conference

  Public discourse


• 重力波が拓く物理学の未来

  早田 次郎

  関西地域セミナー, Jun. 2014, Japanese, 神戸大学, Domestic conference

  [Invited]

  Invited oral presentation


• Quantum Entanglement in de Sitter Space

  早田 次郎

  Workshop for String Theory and Cosmology, Jun. 2014, English, 釜山, International conference

  [Invited]

  Invited oral presentation


• ドジッター時空のエンタングルメントエントロピー

  早田 次郎

  日本物理学会, Mar. 2014, Japanese, 東海大学, Domestic conference

  Oral presentation


• A Challenge to Cosmic No-hair

  早田 次郎

  ケープタウン大学セミナー, Mar. 2014, English, ケープタウン(南アフリカ), International conference

  Public discourse


• Gauge Fields and Cosmic No-Hair Conjecture 2

  早田 次郎

  国立清華大学, Dec. 2013, English, 新竹（台湾）, International conference

  [Invited]

  Invited oral presentation


• Gauge Fields and Cosmic No-Hair Conjecture 1

  早田 次郎

  国立清華大学, Dec. 2013, English, 新竹（台湾）, International conference

  [Invited]

  Invited oral presentation


• 代数幾何学と宇宙論の接点

  早田 次郎

  神戸大学数学科可積分系セミナー, Oct. 2013, Japanese, Domestic conference

  Public discourse


• ゲージ場とインフレーション

  早田 次郎

  国立天文台理論物理学研究, Oct. 2013, Japanese, Domestic conference

  [Invited]

  Invited oral presentation

• The International Society on General Relativity and Gravitation


• 理論天文学宇宙物理学懇談会


• The Physical Society of Japan

• Exploring Physics of High-frequency Gravitational Waves

  早田 次郎, 吉野 裕高, 野海 俊文, 菅野 優美

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Kobe University, 01 Apr. 2022 - 31 Mar. 2026

  現在、干渉計で観測できる重力波は10Hz から1kHz くらいの狭い周波数帯域に限られている。今後、宇宙空間へ干渉計を打ち上げることで1mHz まで周波数帯を低周波側に伸ばす計画はあるが、電磁波を用いた天文学に比べるとまだ十分とは言えない。10kHz から10THz までの周波数帯へ観測領域を広げることで新たな重力波源が見えてくるはずである。本研究計画では、申請者らのマグノンを用いたGHz 重力波検出原理をさらに発展させ高周波重力波物理学を開拓すること、この周波数帯の重要な重力波源として太陽質量より軽い原始ブラックホールを研究すること、重力波を用いてQCDアクシオンを探索することを目的としている。 代表の早田は、イットリウム鉄ガーネット（YIG）強磁性体球を用いた重力波検出可能性を検討し、フェルミ正規座標系を拡張することで格段に精度が向上することを明らかにした。これは将来の高周波重力波検出器をデザインするうえで重要な成果である。分担者の野海は、positivity boundを用いて、暗黒物質の候補であるである暗黒光子のパラメータに対して下限を与えた。これは、実験で得られている上限と組み合わせて暗黒物質解明に重要な示唆を与えている。分担者の菅野は、インフレーション中に発生する重力波が原始磁場によってうける影響を明らかにした。これは高周波重力波観測にとって重要な結果である。分担者の吉野は、回転ブラックホールの周りのアクシオンの不安定性を解析し、ボーズノヴァが起こる可能性があることを示した。このことから、原始ブラックホールからの高周波重力波発生が期待できることがわかった。


• Development of high frequency gravitational wave physics

  早田 次郎, 吉野 裕高, 野海 俊文, 菅野 優美

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Kobe University, 01 Apr. 2022 - 31 Mar. 2026


• Weak gravity conjectue and its application to particle physics and cosmology

  野海 俊文, 早田 次郎, 泉 圭介

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 01 Apr. 2020 - 31 Mar. 2024


• Exploring the origin of CMB anomaly with spontaneous symmetry breaking

  早田 次郎, 野海 俊文

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 01 Apr. 2017 - 31 Mar. 2022, Principal investigator

  
  宇宙マイクロ波背景放射(CMB)観測衛星WMAPによって、CMB温度揺らぎに統計的非等方性などの異常な性質（CMBアノーマリー）が発見された。そのような中、我々は非等方性の生成機構を発見し、CMBアノーマリーの理解に貢献した。本研究では、自発的対称性の破れという観点から、さらにこの研究を発展させ、多様なCMBアノーマリーの物理的機構を明らかにする。その研究成果をもとに新たな現象を予測し、観測の将来計画に指針を与える。さらに、CMBアノーマリーの背後にある初期宇宙を支配する究極理論を探求する。 本年度、研究代表者の早田は、自発的に対称性の破れた背景での原始重力波の統計を調べ、高周波数モードの場合サブポアッソン統計分布を示す可能性があることを示した。古典論的な重力波生成であればサブポアッソン分布は生じないことが分かっているので、これは重力子の観測可能性を示すものであり、画期的な成果である。また、時空のパリティー対称性の破れを重力波の伝搬を通して検証できることを明らかにした。 インフレーション中の宇宙はハッブルスケール程度の温度を持った様々な粒子で満たされている。原始ゆらぎがこれらの熱浴と相互作用していると、粒子生成の効果に伴い非ガウス性などの観測量に影響が現れると期待される。本年度、分担者の野海は、時間並進対称性の自発的破れに基づく「原始ゆらぎの有効場理論」にこのような粒子生成の効果を取り込むことに成功した。構成した有効理論はインフレーションだけでなく時間結晶や同期現象などの物性系への応用も期待される。

  Competitive research funding


• 重力波で探る重力セクターでのパリティーの破れとアクシオンダークマター

  早田 次郎

  日本学術振興会, 科学研究費助成事業 新学術領域研究(研究領域提案型), 新学術領域研究(研究領域提案型), 神戸大学, 01 Apr. 2018 - 31 Mar. 2020, Principal investigator

  宇宙には、暗黒物質（DM）と呼ばれる見えない物質が存在し、その正体を解明することは宇宙論の大問題となっている。DMの候補として最近、軽い質量を持ったアクシオンDMの研究が重要となってきた。アクシオンDMの大きな特徴はアクシオン場のコヒーレントな振動にある。一方、重力波の直接観測が成功したことにより、重力波を用いたアインシュタイン重力を超える理論の探求は大きな課題となっている。ここではアクシオンとの結合が重要となるチャーン・サイモンズ重力理論に着目する。本研究の目的は、チャーン・サイモンズ重力理論におけるブラックホール連星等からの重力波の伝搬がアクシオン振動との相互作用によってどのような影響を受けるのかを研究し、時空のパリティーを破れとアクシオンDMの証拠を明らかにすることである。 1.アクシオンDM環境における重力波伝搬を解析し、結合定数の大きさについて太陽系観測で得られる制限より6桁ほど強い制限が得られることを発見した。アクシオンと重力波の共鳴によって円偏光重力波へと変換されることを明らかにした。また、アクシオンとの結合によって重力波が光速からずれることを明らかにした。 2. アクシオンによるパラメータ共鳴や光速からのずれなどの現象が電磁波においても生じることを明らかにした。 3. 放射優勢期において、アクシオン振動による重力波生成が起き、その信号がLISAなどの宇宙重力波干渉計で観測され得ることを示した。

  Competitive research funding


• Probing quantumness of primordial gravitational waves with quantum information theory

  Soda Jiro

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Challenging Research (Exploratory), Challenging Research (Exploratory), Kobe University, 30 Jun. 2017 - 31 Mar. 2020

  We clarified the importance of Mermin's inequality and the staticis of gravitons for characterizing non-classicality of fluctuations generated during inflation. Inflation predicts that the quantum state of gravitons is a squeezed state. We studied the effect of quantum fluctuations on a heavy particle and showed that the gravitons induce decoherence of the quantum coherence of the particle. Based on our results, we proposed a concrete experimental setup for detecting gravitons. The paper is selected as Editors' suggestion of Phsical Review D. This clearly shows our work is recognized by the community in the world.


• Explaining Accelerating Universe from Ultimate Theory

  Ooguri Hirosi

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), The University of Tokyo, 29 Jun. 2015 - 31 Mar. 2020

  Progress has been made in the Swampland program to give constraints on low energy effective theory of consistent quantum theory of gravity such as string theory. In particular, new Swampland conditions such as "de Sitter condition" and "anti-de Sitter condition" have been proposed. These proposals have made impact on models of elementary particles and cosmology. At the same time, some of Swampland conditions have been placed on more solid foundations. In particular, a rigorous proof was given to the statement that there is no global symmetry in consistent quantum theory of gravity, using the holographic principle. This statement has been debated over 50 years, and our work finally settled the discussion. We also proposed new theoretical models of inflation and dark matter in the Universe.


• 量子情報理論から迫る原始重力波の量子性

  早田 次郎

  学術研究助成基金助成金／挑戦的研究（萌芽）, Apr. 2017 - Mar. 2020, Principal investigator

  Competitive research funding


• Quest for the Ultimate Theory in terms of rich cosmophysical phenomena caused by fields and particles in the hidden sector

  Kodama Hideo, KOBAYASHI Tatsuo, SODA Jiro, MIZOGUCHI Shun'ya, SUMITOMO Yoske, NOZAWA Masato

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Scientific Research (A), 27 Jun. 2014 - 31 Mar. 2018

  We have systematically explored methods to probe whether the unified theory called string theory is the ultimate theory of Nature in terms of observations of phenomena caused by fields and particle in the hidden sector specific to superstring theory. As a result, we have proposed lots of new methods such as the observation of gravitational waves produced by the interaction between black holes and a scalar field called axion, observations of gamma rays from high-energy astrophysical objects and cosmic infrared background radiations, observations of electromagnetic and gravitational waves passing through axion dark matter, new particle searches by accelerator experiments, CMB observations of inflation in the early universe. Further, we have constructed some concrete examples of superstring compactifications that are consistent with both the standard model of elementary particles and cosmology.


• 重力波で探る新たな時空像

  早田 次郎

  日本学術振興会, 科学研究費助成事業 新学術領域研究(研究領域提案型), 新学術領域研究(研究領域提案型), 神戸大学, 01 Apr. 2014 - 31 Mar. 2016, Principal investigator

  ヒッグス粒子が発見され、標準模型の正しさが証明されるとともに、ニュートリノの質量や暗黒物質など、標準模型では説明できない現象がクローズアップされており、ミクロの物理への新しいアプローチが必要とされている。一方で、インフレーションシナリオの正しさが、宇宙背景放射の観測によってほぼ決定的となった。インフレーションを、ミクロの物理を研究するための道具として積極的に使うことができるようになったのである。これは、インフレーション中に生成された揺らぎ、特に原始重力波、が高エネルギー宇宙の情報をもたらすからである。本研究の目的は、原始重力波を使ったアキシオンセクターの物理の研究であり、それを通して 新たな時空像に迫ることにあった。 今年度は、アキシオンと非アーベルゲージ場の相互作用に加えて、ディラトン場とそのゲージ場への結合関数を導入することで宇宙背景放射の観測と矛盾する事無く、干渉計による重力波観測やパルサータイミングアレイによる重力波観測によって検証し得る大きさの原始重力波が自然に生成される事を示した。超重力理論においてはこのようなモデルは自然であり、重力波による超重力理論の検証を可能にする成果である。また、このとき生成される重力波はパリティー対称性を破った円偏極重力波であり、宇宙初期に時空のパリティー対称性が破れているという興味深い現象を予言している。観測によって実証されれば、新たな宇宙描像を与えるという異議を持っている。
  

  Competitive research funding


• Non-gaussianity in anisotropic inflation

  Soda Jiro

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 01 Apr. 2013 - 31 Mar. 2016, Principal investigator

  We calculated the non-gaussianity in anisotropic inflation systematically. In addition to the non-gaussianity, we have also evaluated the spectral index and the tensor-scalar ratio in anisotropic inflation. Then, we compared those with Planck data. Consequently, we succeeded in putting constraints on the model parameters in anisotropic inflation. In the previous studies in anisotropic inflation, a specific functional relation between the potential function of inflaton and the gauge kinetic function had been assumed. In order to reveal universality of the anisotropic inflation, we considered more general potential function and the gauge kinetic function. As a result, we have shown that the anisotropic inflation can generically occur for some short period during inflation or in the last stage of inflation. This clearly shows the universality of the anisotropic inflation.

  Competitive research funding


• research on cosmological nonlinear and non-perturbative gravitational phenomena

  SASAKI Misao, TANAKA Takahiro, SHIROMIZU Tetsuya, SODA Jiro, MUKOHYAMA Shinji, MATSUBARA Takahiko, TAKAHASHI Fuminobu, CHIBA Takeshi, TSUJIKAWA Shinji, ISHIHARA Hideki, YAMAMOTO Kazuhiro, YAMAGUCHI Masahide

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Scientific Research (A), Kyoto University, 01 Apr. 2009 - 31 Mar. 2015

  It is believed that the universe has undergone a stage of accelerated expansion, an inflationary stage, right after the birth, and all the fluctuations that are responsible for the structure of the universe today were generated during this stage. One of the most important issues in cosmology is to understand how these fluctuations have evolved to the large scale structure of the universe such as galaxies through nonlinear and non-perturbative gravitational phenomena. In this project, we have systematically investigated various types of fluctuations, from microscopic quantum fluctuations to macroscopic fluctuations of spacetime, and obtained many world top-class results. These results form an important basis for the future direction of research in cosmology.


• The exploration of extradimensions in terms of a variety of cosmophysical phenomena caused by axionic moduli

  KODAMA Hideo, OHTA Nobuyoshi, TAKAHASHI Fuminobu, NAKAYAMA Kazunori, OHTA Nobuyoshi, SHIBATA Masaru, MIZOGUCHI Shun'ya, KOBAYASHI Tatsuo, SODA Jiro, KOHRI Kazunori, ISHIBASHI Akihiro, IOKA Kuninito, TAKAHASHI Fuminobu, YOSHINO Hirotaka, NOZZWA Masato, NAGATA Ryo, KAWANAKA Norita, TOMIZAWA Shin'ya

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Scientific Research (A), High Energy Accelerator Research Organization, 01 Apr. 2010 - 31 Mar. 2014

  In order to open up a new observational/experimental window to the ultimate theory, we have studied axions from both the cosmophysics phenomenology aspect and the superstring/supergravity aspect and have published more than 200 papers. The main achievements are demonstarations of the axion bose nova phenemenon caused by a rotating black hole by numerical simulations and the discovery of its observability by gravitational wave experiments, derivation of a parameter range for axion to resolve the conflict between the high energy gamma-ray observations and the infrared background observation, evaluations of the influences of axions produced by the decay of heavy moduli on cosmic microwave background and derivation of constraints on the compactification of extra-dimensions on the basis of this estimation, derivation of constraints on elementary particle models from cosmological influences of axionic isocurvature perturbations and topological defects.


• Quest for the ultimate theory on the basis of direct observations of the early evolution of the universe

  KODAMA Hideo, KAWASAKI Masahiro, YOKOYAMA Jun'ichi, SODA Jiro, TSUJIKAWA Shinji, MUKOHYAMA Shinji, NAKAYAMA Kazunori, KITAZAWA Yoshihisa, CHIBA Takeshi, SHIROMIZU Tetsuya, TANAKA Takahiro, KOHRI Kazunori, TAKAHASHI Fuminobu, NOZZWA Masato, NAKAYAMA Kazunori

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), High Energy Accelerator Research Organization, 23 Jul. 2009 - 31 Mar. 2014

  In this project, we have pushed forward investigations from the two different directions, the phenomomenology of the universe focused on cosmological fluctuations and the construction of universe models based on unified theories including gravity, and published more than 300 papers. The most significant resutls are the construction of the most general inflation theory with a single driving scalar field and the comparison of its predictions with observations, the construction of a consistent anisotropic inflation model and the derivation of its detailed observational predictions, the construction of a variety of large field inflation models on the basis of 4D supergravity unified theories, derivation of constraints on elementary particle theory on the basis of investigations of axion cosmology by 3D numerical simulations, clarification of the IR divergence problem in quantum correstions to inflation, and systematic studies of various modified gravity theories.


• Anisotropic inflation from supergravity

  SODA Jiro

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kyoto University, 2010 - 2012

  It is known that there exists a non-trivial coupling between scalar fields and kinetic terms of gauge fields. Based on this fact, we found a novel inflationary scenario, the so-called anisotropic inflation. We succeeded in clarifying the existence of the statistical anisotropy in the cosmic microwave temperature fluctuations and the cross correlation between the temperature fluctuations and polarizations. Although we could not prove our model using cosmological data due to the delay of the data release by the Planck team, I am sure we opened a new window for exploring fundamental theory of nature through the cosmological data stemmed from the early universe.


• 超重力理論から創出される非等方インフレーション宇宙の研究

  早田 次郎

  文部科学省, 科学研究費補助金(基盤研究(C)), 2010 - 2012, Principal investigator

  Competitive research funding


• 宇宙初期進化の直接観測に基づく究極理論探査

  小玉 英雄

  文部科学省, 科学研究費補助金(新学術領域研究(研究領域提案型)), 2009 - 2012

  1. 宇宙初期におけるゆらぎの生成とCMB観測(1) 局所ボイド宇宙モデルにおいて,中心からずれた位置で観測されるCMB温度非等方性に対する双極成分および4重極成分に対する一般的な解析的公式を初めて導出.双極成分と異なり4重極成分の大きさはボイドサイズに大きく依存することを発見.さらに,偏光に対する重力レンズ効果を与える解析表式を導出し,ボイドが特有のE-B相関を生み出すことを指摘.2編の論文を準備中[小玉,齋藤,後藤](2) ドメインウォールの時間発展を高精度で数値計算し,それに基づいてドメインウォールからの重力波を評価.また,コスミックストリングのキンクからの重力波放出量を評価し,さらにこの重力波が生み出すBモードの相関関数を計算.[川崎,平松,齊川,宮本,中山](3) 最大尤度反転法によるりCMB非等方性観測データから初期曲率ゆらぎのパワースペクトルを再構築し,それに基づいたMCMC法により初期パワースペクトルアノマリーを発見[市來,永田,横山].(4) 密度ゆらぎが2

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• カルツァ・クライン・ブラックホールの古典及び量子論的側面

  早田 次郎, KONOPLYA Roman, ROMAN Konoplya

  日本学術振興会, 科学研究費助成事業 特別研究員奨励費, 特別研究員奨励費, 京都大学, 2007 - 2009

  高次元ブラックホールは弦理論の予言の1つであり、加速器実験において重要な役割を果たす可能性がある。特に、その安定性は重要な研究テーマとなっている。 我々はすでにKaluza-Kleinブラックホールや特殊な回転するブラックホールの安定性を示すことに成功している。本年度は、さらに、高次元ブラックホールの安定性に関して重要な発見をした。Einsteinの重力理論の自然な拡張であるLovelock重力と呼ばれる高階微分の入った理論におけるブラックホールの安定性の解析を行い、質量が小さなブラックホールが偶数次元では不安定性を示すことを明らかにした。特に、短波長で強い不安定性を示すことを発見した。このような現象はEinsteinの重力理論では見られない。高階微分は量子重力理論による補正とみなすことこともできるが、我々の発見はこのような摂動的な重力理論の記述が破綻する可能性があることを示しており、弦理論などの基礎理論を構築するうえでも、非常に重要な示唆を与えるものと思われる。 また、加速器実験でつくられるかもしれない高次元の回転するブラックホールからの重力子のホーキング放射を計算することに成功した。このような計算は実際にデータと比較してブラックホール生成の有無を判定するために重要となるであろう。


• A Possible Lorentz Violation and Its Impact on Cosmology

  SODA Jiro

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kyoto University, 2006 - 2009

  Due to developments of observations, it becomes important to check the fundamental principle such as Lorentz invariance. Moreover, precision cosmology urged us to study theoretical fine structure. However small it is, it is worth exploring in detail. Based on this motivation, we have studied the impact of Lorentz violation on cosmology. We found an anisotropic inflationary scenario where Lorentz invariance is spontaneously broken. We also formulated cosmological perturbation theory in this background and succeeded in making predictions for various observables relevant to future observations of cosmic microwave background radiation.


• A Possible Lorentz Violation and Its Impact on Cosmology

  Jiro SODA

  Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), 2006 - 2009, Principal investigator

  Due to developments of observations, it becomes important to check the fundamental principle such as Lorentz invariance. Moreover, precision cosmology urged us to study theoretical fine structure. However small it is, it is worth exploring in detail. Based on this motivation, we have studied the impact of Lorentz violation on cosmology. We found an anisotropic inflationary scenario where Lorentz invariance is spontaneously broken. We also formulated cosmological perturbation theory in this background and succeeded in making predictions for various observables relevant to future observations...

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• Research on the possibility of experimentally/observationally verifying higher dimensional theory of spacetime

  SASAKI Misao, KODAMA Hideo, SHIBATA Masaru, SHIROMIZU Tetsuya, SODA Jiro, TANAKA Takahiro, NAKAO Ken-ichi, NAKAMURA Takashi, YOKOYAMA Jun'ichi

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kyoto University, 2005 - 2008

  高次元時空理論に基づく宇宙論やブラックホール形成問題を詳しく解析し、それらがどのような実験ないしは観測によって検証可能かを研究した。その結果、宇宙論においては、宇宙曲率揺らぎの非ガウス性が重要であるという共通認識を得た。そこで、非ガウス性を一般的に取り扱う定式化を構築した。また、高次元ブラックホールに関しては、LHCにおけるブラックホール生成条件等に関するより定量的な評価を導出した。


• Research on the possibility of experimentally/observationally verifying higher dimensional theory of spacetime

  Misao SASAKI

  Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), 2005 - 2008

  高次元時空理論に基づく宇宙論やブラックホール形成問題を詳しく解析し、それらがどのような実験ないしは観測によって検証可能かを研究した。その結果、宇宙論においては、宇宙曲率揺らぎの非ガウス性が重要であるという共通認識を得た。そこで、非ガウス性を一般的に取り扱う定式化を構築した。また、高次元ブラックホールに関しては、LHCにおけるブラックホール生成条件等に関するより定量的な評価を導出した。

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• Detecting Extra-dimensions through Cosmic Background Radiation

  SODA Jiro

  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kyoto University, 2002 - 2005

  Recent observation on cosmic background radiation by WMAP strongly supports the validity of the inflationary scenario. Nowadays, the most important issue in theoretical cosmology is to unveil the inflaton. On the other hand, it is widely believed that the superstring theory is the most promising candidate of the ultimate unified theory of everything. The most precise prediction of superstring theory is that our world is 10-dimensions. That means the extra 6-dimensions must be compactified to the small size to reconcile with our real world. Recent developments of superstring theory suggest the braneworld picture as a mechanism of compactification. We have unveiled the inflaton based on this new picture of the world, namely braneworld. Firstly, we have constructed the 4-dimensional effective theory describing the low energy dynamics of the braneworld by using the gradient expansion method invented by us. Then, using this effective theory, we have analyzed the collision process of two braneworlds. At the collision point, we have utilized the purely 5-dimensional analysis. The point is that we have constructed the geometrical inflation model. In our inflationary model, Inflation is caused by the flux in the bulk and terminated by the collision of braneworlds. The heat produced by the collision ignites the big-bang of our universe. We have also calculated the cosmological perturbations produced by the quantum process during rapid expansion and shown that the predictions are consistent with the present observations.


• Detecting Extra-dimensions through Cosmic Background Radiation

  Jiro SODA

  Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(C)), 2002 - 2005, Principal investigator

  Recent observation on cosmic background radiation by WMAP strongly supports the validity of the inflationary scenario. Nowadays, the most important issue in theoretical cosmology is to unveil the inflaton. On the other hand, it is widely believed that the superstring theory is the most promising candidate of the ultimate unified theory of everything. The most precise prediction of superstring theory is that our world is 10-dimensions. That means the extra 6-dimensions must be compactified to the small size to reconcile with our real world. Recent developments of superstring theory suggest t...

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• 宇宙の構造形成と超弦理論による宇宙の特異点の解消

  早田 次郎

  日本学術振興会, 科学研究費助成事業 奨励研究(A), 奨励研究(A), 京都大学, 1998 - 1999

  我々の宇宙はビッグバンモデルによって記述されると信じられている。ただし、この理論には初期特異点の問題がある。ほとんどの人は、この問題が量子重力理論によって解決されると期待している。本研究の目的はこの問題と宇宙の構造形成の問題とを結び付けて考察することであった。現在、量子重力理論の候補としては超弦理論しか存在しない。そこでこの理論の中で、初期特異点の存在しないような宇宙モデルを研究することから出発した。弦理論における量子補正を考慮したモデルの線形安定性を調べることで、新しい種類の不安定性を発見した。さらに詳しくモデルを調べることで、新しい宇宙の創世の機構を明らかにした。 また、最近の観測から宇宙の曲率が負であることが明らかになったが、我々は特異点を持たない開いた宇宙の生成機構を研究し、トンネル効果で宇宙が生まれ、同時にインフレーションが起きうることを示した。一方で、双対性との関連で我々が高次元の中のブレインに住んでいるという描像がどんな宇宙的帰結が得られるかを調べた。その結果、我々の宇宙が無の状態からトンネル効果によって生み出されるという描像が普遍的であることを明らかにした。 今後は、これらの成果を超弦理論の立場から整理統合していく計画である。


• 宇宙の構造形成と超弦理論による宇宙の特異点の解消

  早田 次郎

  文部科学省, 科学研究費補助金(奨励研究(A)), 1998 - 1999, Principal investigator

  我々の宇宙はビッグバンモデルによって記述されると信じられている。ただし、この理論には初期特異点の問題がある。ほとんどの人は、この問題が量子重力理論によって解決されると期待している。本研究の目的はこの問題と宇宙の構造形成の問題とを結び付けて考察することであった。現在、量子重力理論の候補としては超弦理論しか存在しない。そこでこの理論の中で、初期特異点の存在しないような宇宙モデルを研究することから出発した。弦理論における量子補正を考慮したモデルの線形安定性を調べることで、新しい種類の不安定性を発見した。さらに詳しくモデルを調べることで、新しい宇宙の創世の機構を明らかにした。また、最近の観測から宇宙の曲率が負であることが明らかになったが、我々は特異点を持たない開いた宇宙の生成機構を研究し、トンネル効果で宇宙が生まれ、同時にインフレーションが起きうることを示した。一方で、双対性との関連で我々が高次元

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• 非一様宇宙の量子論

  早田 次郎

  日本学術振興会, 科学研究費助成事業 奨励研究(A), 奨励研究(A), 京都大学, 1995 - 1995

  この研究の目的は宇宙の大規模構造の起源を量子重力にまでさかのぼって明らかにすることにあった。特に、そのための道具として微分展開法を適用しようと計画していた。 手始めに、微分展開法の数学的な側面を正準形式との関連で研究した。その成果として、ブランス-ヂッケ理論における微分展開法を開発することができた。それにより、重力定数の非一様性がどうゆうふうに成長するのかを明らかにすることができた。また、物理的側面としては、通常の摂動法との関係を具体的に示すことに成功した。さらに、現在座標系によらない摂動計算法の開発を進めており、この方法の有効性を明らかにしていく予定である。 上の研究とは別に、比較的現在に近い時代の密度揺らぎの成長の問題を研究した。 この研究では,逓減摂動法によって弱非線形効果を取り入れて問題を非線形シュレデインガー方程式に帰着させた。その成果として、密度揺らぎの成長の新しい機構が存在することを示した。 ところで、ガルザ-クライン理論では、インフレイションが終わらずに時空が不安定であることが知られている。この宇宙初期における時空の不安定性の問題も宇宙の起源の問題として重要であるが、我々はそれを解決するために正準交換関係の変更を提案し、実際このときに不安定性が回避されることを示した。 さらに、これらの理論的な研究と観測との比較のためのデータ解析の新しい方法の開発も研究している。その結果ウェーブレット解析を利用した非線形解析が有効であることをあきらかにすることができている。現在、ウェーブレット解析を利用した新しい統計量の有効性を研究中である。


• 非一様宇宙の量子論

  早田 次郎

  文部科学省, 科学研究費補助金(奨励研究(A)), 1995 - 1995, Principal investigator

  この研究の目的は宇宙の大規模構造の起源を量子重力にまでさかのぼって明らかにすることにあった。特に、そのための道具として微分展開法を適用しようと計画していた。手始めに、微分展開法の数学的な側面を正準形式との関連で研究した。その成果として、ブランス-ヂッケ理論における微分展開法を開発することができた。それにより、重力定数の非一様性がどうゆうふうに成長するのかを明らかにすることができた。また、物理的側面としては、通常の摂動法との関係を具体的に示すことに成功した。さらに、現在座標系によらない摂動計算法の開発を進めており、この方法の有効性を明らかにしていく予定である。上の研究とは別に、比較的現在に近い時代の密度揺らぎの成長の問題を研究した。この研究では,逓減摂動法によって弱非線形効果を取り入れて問題を非線形シュレデインガー方程式に帰着させた。その成果として、密度揺らぎの成長の新しい機構が存在することを

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• 自明でないトポロジーを持つ非等方宇宙における重力波

  早田 次郎

  日本学術振興会, 科学研究費助成事業 奨励研究(A), 奨励研究(A), 京都大学, 1994 - 1994

  第一の目的は、宇宙論的スケールの重力波が宇宙の非等方性やトポロジーによってどのような影響を受けるのかを明らかにすることであった。この目的のために、具体的なモデルを構成する必要性があった。まず、4次元時空に平面対称性を課し、さらに対称性のある面に対して周期境界条件を課してトーラス的なトポロジーを持った時空を構成した。このモデルは非等方性も持っており今の目的にかなったものである。 次に、このモデルに関するアインシュタイン方程式を解くことにより宇宙の時間発展を明らかにした。さらに、こうして構成された背景時空上で摂動を考えることにより重力波を考察した。 解析の結果を理解するには、背景場の性質をタイヒミューラーパラメーターと呼ばれるトーラスの形を特徴づける量で表現するとよい。背景場のトーラス部分のツウィストがないような時空の時間発展を考えると、その上の重力波は背景場の影響で振幅を変化させるが偏極は独立性を保ったままであることがわかった。一方、背景場のトーラス部分のツウィストが時間とともに変化するような場合、重力波は振幅を変化させるとともにその偏極がまざりあうという現象がおきることが明らかになった。 このことから、宇宙論的なスケールの重力波の偏極の様子を観測すると宇宙の非等方度やトポロジーを知ることができるのではないかと考えられる。実際には、膨張宇宙での重力波の量子力学的生成率を計算し、その強度や偏極を知ることが必要となる。さらに、それとCOBEの観測データを比較することにより我々の宇宙のトポロジーが決定できるはずである。この点に関してはまだ研究中であり結果を出すまでにはいたっていない。


• 自明でないトポロジーを持つ非等方宇宙における重力波

  早田 次郎

  文部科学省, 科学研究費補助金(奨励研究(A)), 1994 - 1994, Principal investigator

  第一の目的は、宇宙論的スケールの重力波が宇宙の非等方性やトポロジーによってどのような影響を受けるのかを明らかにすることであった。この目的のために、具体的なモデルを構成する必要性があった。まず、4次元時空に平面対称性を課し、さらに対称性のある面に対して周期境界条件を課してトーラス的なトポロジーを持った時空を構成した。このモデルは非等方性も持っており今の目的にかなったものである。次に、このモデルに関するアインシュタイン方程式を解くことにより宇宙の時間発展を明らかにした。さらに、こうして構成された背景時空上で摂動を考えることにより重力波を考察した。解析の結果を理解するには、背景場の性質をタイヒミューラーパラメーターと呼ばれるトーラスの形を特徴づける量で表現するとよい。背景場のトーラス部分のツウィストがないような時空の時間発展を考えると、その上の重力波は背景場の影響で振幅を変化させるが偏極は独立性

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• 重力理論の量子化と自明でないトポロジーを持つ空間における場の理論

  早田 次郎

  日本学術振興会, 科学研究費助成事業 奨励研究(特別研究員), 奨励研究(特別研究員), 広島大学, 1990 - 1990