Theoretical physics · Cosmology

Atsuhisa Ota

Associate Professor School of Physics, Chongqing University

aota [at] cqu.edu.cn ORCID GitHub INSPIRE Google Scholar researchmap

About me

  • I do research in theoretical physics in Chongqing, China.
  • My field is cosmology and the non-equilibrium systems related to it.
  • I love cats and a good drink.
COSMOLOGYwe see the past light coneSYMMETRYV(φ) = λ(|φ|² − v²)²GRAVITATIONAL WAVESδL/L = ½ h₊EFFECTIVE FIELD THEORYℒ = Σᵢ cᵢ Oᵢ / ΛΔᵢ−4​zoom out: UV → IRINFLATIONa ∝ eN​, N = number of e-foldsN=0N=1N=2OPEN QUANTUM SYSTEMρ_S = Tr_E ρPERTURBATION THEORYδ ≪ 1z zbackground + small ripplesFLUCTUATION–DISSIPATIONτ ∼ τ + β (KMS)fluctuationdissipationβ
Swipe to see the whole picture →
  • Cosmology
  • Symmetry
  • Gravitational waves
  • Effective field theory
  • Inflation
  • Open quantum systems
  • Cosmological perturbation theory
  • Fluctuation–dissipation relation

Research Interests

I believe the appeal of theoretical physics lies in its power to depict, through theory, a world that we cannot see directly. Testing by experiment and observation is indispensable, but what excites me most is that theory can predict and understand a world that has not yet been seen.

For me, the foremost example is the universe itself. The matter and radiation in the universe carry slight unevenness in density and temperature, and spacetime itself fluctuates, with its ripples traveling as gravitational waves. How these fluctuations were born and how they have evolved reflect the state of the early universe and the properties of the matter in it. Through cosmological perturbation theory, which computes their time evolution, I have been tracing the picture of the beginning of the universe.

Selected Results

01Gravitational waves in a dynamical radiation background

  • Formulated the linear response of gravitational waves in a dynamical radiation background in quantum field theory, for fields of spin 0, 1/2 and 1.
  • Derived, in the real-time formalism, the kinetic response theory based on the Vlasov equation as the hard-thermal-loop limit.
  • Organized the constraints that symmetry places on this response on a dynamical background, from the viewpoint of the ambiguity under field redefinitions.

arXiv:2510.22346arXiv:2601.03631

02Renormalizing the gravitational-wave response of resonant matter

  • Renormalized the linear response of gravitational waves in a scalar field that depends explicitly on time and is amplified by resonance.
  • For the ultraviolet divergences of the one-loop response, proposed an adiabatic regularization that takes the coincidence limit in real time.
  • Showed that the time dependence produces new local divergences, and identified the counterterms.

arXiv:2606.16296

03Stability of charged relativistic hydrodynamics

  • Studied general first-order relativistic viscous hydrodynamics with a U(1) charge in the framework of infrared effective field theory for dissipative fluids.
  • Analyzed its dispersion relations consistently in the gradient expansion, starting from the most general quadratic action with noise.
  • Proved that, under unitarity and the KMS conditions, it is stable in any inertial frame and any fluid frame as long as the enthalpy is positive.

arXiv:2410.23837

04Spontaneous breaking of time translation in open systems

  • In open systems with fluctuation and dissipation, the time-translation symmetry doubled in the Schwinger–Keldysh formalism is broken down to its diagonal part.
  • Built on this symmetry structure, constructed the effective field theory of Nambu–Goldstone modes in phases where time translation is spontaneously broken.
  • The framework has in view applications to synchronization, time crystals and cosmic inflation.

arXiv:1805.06240

Publications

From INSPIRE-HEP

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Curriculum Vitae

Research positions

  1. Sep 2023 – presentAssociate ProfessorSchool of Physics, Chongqing University
  2. Sep 2021 – Aug 2023IAS Postdoctoral FellowHKUST Jockey Club Institute for Advanced Study
  3. Apr 2020 – Aug 2021Postdoctoral ResearcherDepartment of Physics and Astronomy, Ohio University
  4. Apr 2018 – Mar 2020JSPS Overseas Research FellowDAMTP, University of Cambridge
  5. Apr 2017 – Mar 2018JSPS Research Fellow (PD)Tokyo Institute of Technology
  6. Apr 2016 – Mar 2017JSPS Research Fellow (DC2)Tokyo Institute of Technology

Education

  • Mar 2017Ph.D. in Physics, Tokyo Institute of Technology
  • Mar 2014M.S. in Physics, Tokyo Institute of Technology
  • Mar 2012B.S. in Physics, Tokyo Institute of Technology

Memberships

  • 2025 (rejoined) – presentThe Physical Society of Japan
  • Nov 2014 – presentRironkon (Theoretical Astrophysics Society of Japan)
  • Dec 2019 – presentUK Cosmology
  • Apr 2020 – Sep 2021Dark Energy Spectroscopic Instrument (DESI) Collaboration

Grants and fellowships

  • Jan 2025 – Dec 2027National Natural Science Foundation of China, Young Scientists Fund (Category C) PI
  • Jan 2025 – Dec 2027Chongqing New YC Project PI
  • Apr 2018 – Mar 2020JSPS Overseas Research Fellowship
  • Apr 2016 – Mar 2018JSPS KAKENHI Grant-in-Aid for JSPS Fellows (DC2, then PD) PI

Teaching

  • Mar 2026 – presentCosmology (graduate), Chongqing University Lecturer in English own lecture notes
  • Mar 2024 – AY2025Introduction to Astrophysics (graduate), Chongqing University Lecturer in English own lecture notes
  • Sep 2024 – presentIntroduction to Quantum Information Theory (graduate), Chongqing University Lecturer in English
  • 2025Effective theory of hydrodynamic modes, Saga University Intensive lecture course
  • 2013 – 2016Analytical Mechanics (problem sessions), Dept. of Physics, Tokyo Institute of Technology Teaching assistant
  • 2013 – 2016Electromagnetism (problem sessions), Dept. of Physics, Tokyo Institute of Technology Teaching assistant
  • 2013 – 2014Physics B and C (university-wide physics problem sessions), Tokyo Institute of Technology Teaching assistant
  • during Ph.D.Academic Presentation (graduate), Tokyo Institute of Technology Teaching assistant

Languages

  • Japanese native
  • English fluent

Talks

Invited talks11
  1. 21 Oct 2026Is First-Order Hydrodynamics Really Unstable? - Mode Analysis as an IR Effective TheoryC3NT Workshop on QCD Critical End Point and Effective Field Theory Methods (CEP-EFT 2026) · Central China Normal University (CCNU), Wuhan, China
  2. 6 Aug 2026Frame invariant analysis of first order hydrodynamics as IR effective theoryQuantum crossroads: Interdisciplinary, hybrid workshop at the interface of open quantum systems, high-energy physics, and quantum science · Kavli IPMU, Kashiwa, Japan
  3. 30 Oct – 3 Nov 2025Gravitational waves in thermal environmentsWorkshop on Gravitational Waves, Cosmology and Fundamental Physics · Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
  4. 31 Aug – 4 Sep 2025Cosmological stimulated emissionThe 3rd International Workshop on Gravitational Waves and the Early Universe (GWEU25) · Ningbo, China
  5. 31 Jul 2025Cosmological stimulated emissionIBS CTPU-CGA 2025 Summer School and Workshop for High Energy Physics and Cosmology in Korea · Best Western Hotel, Jeonju, Korea
  6. 7 Nov 2024Radiation exchange in primordial gravitational wavesEvolution of the inhomogeneous universe: From Inflation to structure formation · KEK Tsukuba Campus, Tsukuba, Japan
  7. 13–16 Oct 2023Radiation exchange for gravitational wave equal time power spectrumInternational Mini Workshop on Gravitational Waves from the Early Universe · Institute of Theoretical Physics, CAS (co-hosted with the Center for High Energy Physics, Peking University), Beijing, China
  8. 12–14 Dec 2022Scale-invariant enhancement of gravitational waves during inflationMessengers of the very early universe: Gravitational Waves and Primordial Black Holes · Centro Universitario Padovano, Padova, Italy
  9. Oct 2022Scale-invariant enhancement of gravitational waves during inflationEarly Universe and AliCPT Forum · onlineRecording
  10. 13 Mar 2018CMB spectroscopy for primordial non-GaussianityProbing fundamental physics with CMB spectral distortions · CERN, Geneva, SwitzerlandRecording
  11. Dec 2014CMB μ distortion from primordial gravitational wavesMini-Workshop on Cosmology · Asia Pacific Center for Theoretical Physics (APCTP), Korea
Talks at conferences and workshops21
  1. 17 Sep 2026Real-time linear response for gravitational perturbationsHot topics in Modern Cosmology, Spontaneous Workshop XVIII (SW18) · Institut d'Études Scientifiques de Cargèse (IESC), Cargèse, France
  2. 3 Jul 2026Stability analysis of first order hydrodynamics as IR effective theoryContours 2026 – Effective Field Theories Meet the Schwinger–Keldysh Formalism · DAMTP, University of Cambridge, Cambridge, UK
  3. 23 Jan 2026Gravitational waves in thermal environmentsJGRG34: The 34th Workshop on General Relativity and Gravitation in Japan · Yukawa Institute for Theoretical Physics, Kyoto University (Maskawa Hall), Kyoto, Japan
  4. 9 Jul 2025Cosmological stimulated emissionInternational Symposium on Cosmology and Particle Astrophysics (CosPA 2025) · IBS Science Culture Center, Daejeon, Korea
  5. 25 Jun 2025Graviton hard thermal loop5th Mini-workshop on the Early Universe · Ichinoseki, Iwate, Japan
  6. 21–25 Oct 2024Radiation exchange in primordial gravitational wavesCOSMO'24: 27th International Conference on Particle Physics and Cosmology · Kyoto, Japan
  7. 8–14 Sep 2024Radiation exchange in primordial gravitational wavesDSU2024: 18th International Workshop on the Dark Side of the Universe · Corfu, Greece
  8. 14–18 Jun 2024Radiation exchange in primordial gravitational wavesInternational Symposium on Cosmology and Particle Astrophysics (CosPA 2024) · hosted by Ningbo University (InterContinental Ningbo), Ningbo, China
  9. 27 Nov – 1 Dec 2023One-loop thermal radiation exchange in gravitational wave power spectrumJGRG32: The 32nd Workshop on General Relativity and Gravitation in Japan · Sakata-Hirata Hall, Nagoya University, Nagoya, Japan
  10. 18–20 Nov 2023Radiation exchange for gravitational wave equal time power spectrumInternational Conference on Modified Gravity 2023 (MOGRA 2023) · Central China Normal University, Wuhan, China
  11. Oct 2021Gauge invariant formulation of the induced gravitational wavesCopernicus Webinar and Colloquium Series · online
  12. 8–9 Jan 2020Cosmology with the thermal-kinetic Sunyaev-Zel'dovich effectUK Cosmology Meeting 2020 · Lancaster University, Lancaster, UK
  13. 13 Sep 2019CMB spectroscopy at third order in cosmological perturbationsWorkshop on the non-Gaussian Universe · Centre for Theoretical Cosmology, DAMTP, University of Cambridge, Cambridge, UK
  14. 4–8 Mar 2019Statistical anisotropy in CMB spectral distortionsAccelerating Universe in the Dark · Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, Japan
  15. Jan 2018Effective field theory of time-translational symmetry breaking in open systemsInfrared physics of gauge theories and quantum dynamics of inflation · Shiga, Japan
  16. 27 Nov – 1 Dec 2017Spontaneous symmetry breaking in open systems: Toward application to EFT of inflationJGRG27: The 27th Workshop on General Relativity and Gravitation in Japan · Hiroshima University, Higashi-Hiroshima, Japan
  17. 24–28 Oct 2016Cosmological constraints from μE cross-correlationsJGRG26: The 26th Workshop on General Relativity and Gravitation in Japan · Osaka City University, Osaka, Japan
  18. 18–23 Sep 2016Cosmological constraints from μE cross-correlationsSymmetries, Fundamental Interactions and Cosmology 2016 (summer school) · Frauenwörth (Chiemsee), Germany
  19. Aug 2016Cosmological constraints from μE cross-correlationsRESCEU Summer School 2016 · Nagano, Japan
  20. 10–14 Nov 2014CMB μ distortion from primordial gravitational wavesJGRG24: The 24th Workshop on General Relativity and Gravitation in Japan · Kavli IPMU, Kashiwa, Japan
  21. Aug 2014CMB μ distortion from primordial gravitational wavesRESCEU Summer School 2014 · Nagano, Japan
Talks at the Physical Society of Japan meetings5
  1. 12–15 Sep 2017Secondary isocurvature perturbations from acoustic reheatingJPS Autumn Meeting 2017 · Utsunomiya University, Japan
  2. 17–20 Mar 2017CMB spectral distortions as solutions of the Boltzmann equationThe 72nd JPS Annual Meeting · Osaka University, Toyonaka Campus, Japan
  3. 21–24 Mar 2015ガウス統計の2乗に従う等曲率ゆらぎの観測的な帰結Observational consequences of isocurvature perturbations obeying squared Gaussian statisticsThe 70th JPS Annual Meeting · Waseda University, Japan
  4. 18–21 Sep 2014宇宙マイクロ波背景放射のμ歪みと原始重力波CMB μ distortion and primordial gravitational wavesJPS Autumn Meeting 2014 · Saga University, Japan
  5. 26–29 Mar 2013CMBμ-distortionによる初期ゆらぎの制限Constraints on primordial perturbations from the CMB μ-distortionThe 68th JPS Annual Meeting · Hiroshima University, Japan
Seminars37
  1. 21 Oct 2026Collective properties of gravitational waves in a radiation-dominated universeIOA Seminar · Central China Normal University (CCNU), Wuhan, China
  2. Feb 2026Gravitational Waves in Thermal Environments: Real-Time Linear Response, Ward Identities, and spin effectsKyoto University, Japan
  3. Jun 2025Graviton hard thermal loop revisitedIBS (group seminar), Daejeon, Korea
  4. Jan 2025Mode analysis of hydrodynamical Nambu-Goldstone modesLanzhou University, China
  5. Dec 2024Cosmological stimulated emissionHangzhou Institute for Advanced Study (UCAS), Hangzhou, China
  6. Jul 2024Thermal radiation exchange in primordial gravitational wavesRIKEN, Saitama, Japan
  7. Jul 2024Thermal radiation exchange in primordial gravitational wavesKavli IPMU, Chiba, Japan
  8. Jul 2024Thermal radiation exchange in primordial gravitational wavesUniversity of Tokyo, Komaba, Japan
  9. Dec 2023One-loop thermal radiation exchange in gravitational wave power spectrumC-seminar, Nagoya University, Japan
  10. Aug 2023Revisiting gravitational wave energy density from a covariant perspectiveJoint seminar, Rikkyo University, Japan
  11. Jul 2023Revisiting gravitational wave energy density in a covariant perspectiveIBS, Korea
  12. Dec 2022Scale-invariant enhancement of gravitational waves during inflationTokyo Institute of Technology, Japan
  13. Dec 2022Scale-invariant enhancement of gravitational waves during inflationUniversity of Manchester, UK
  14. Dec 2021Covariant transverse-traceless projection for secondary gravitational wavesUniversity of Science and Technology of China, China
  15. Feb 2021Induced superhorizon tensor perturbations from anisotropic non-GaussianityKavli IPMU, Japan
  16. Dec 2020Induced superhorizon tensor perturbations from anisotropic non-GaussianityUniversité catholique de Louvain, Belgium
  17. Dec 2019Cosmology with the thermal-kinetic Sunyaev-Zel'dovich effectUniversity College London, UK
  18. May 2019Statistical anisotropy in spectral distortionsQueen Mary University of London, UK
  19. Mar 2019Statistical anisotropy in spectral distortionsNagoya University, Japan
  20. Dec 2018Statistical anisotropy in spectral distortionsUniversity of Sussex, UK
  21. Nov 2018CMB spectral distortions in the framework of cosmological perturbation theoryUniversity of Manchester, UK
  22. Oct 2018Statistical anisotropy in spectral distortionsInstitute of Cosmology and Gravitation, University of Portsmouth, UK
  23. Oct 2018EFT of dissipative fluid: an application to cosmologyInstitut d'Astrophysique de Paris, France
  24. Oct 2018EFT of dissipative fluid: an application to cosmologyAix-Marseille University, France
  25. May 2018Late time evolution of isocurvature perturbations at second orderUniversity of Padova, Italy
  26. May 2018Late time evolution of isocurvature perturbations at second orderUniversity of Groningen, Netherlands
  27. Apr 2018Open system effective field theory for time-translational symmetry breaking: towards application to EFT of inflationUtrecht University, Netherlands
  28. May 2017A new method for higher order CMB anisotropyRikkyo University, Japan
  29. Mar 2017A new method for higher order CMB anisotropyKobe University, Japan
  30. Mar 2017CMB spectral distortions as solutions to the Boltzmann equationsKEK, Japan
  31. Jan 2017Higher order anisotropies in the cosmic microwave backgroundMax Planck Institute for Astrophysics, Germany
  32. Oct 2016Cosmological constraints from μE cross-correlationsSyracuse University, USA
  33. Oct 2016Cosmological constraints from μE cross-correlationsUniversity of Manchester, UK
  34. Sep 2016Cosmological constraints from μE cross-correlationsUtrecht University, Netherlands
  35. Sep 2016Cosmological constraints from μE cross-correlationsMax Planck Institute for Astrophysics, Germany
  36. Sep 2014The cosmic microwave background μ-distortions and primordial gravitational wavesNagoya University, Japan
  37. May 2014CMB μ distortion and primordial gravitational wavesJoint Seminar, Tokyo Institute of Technology, Japan

Software

Papurr

A Chrome extension that keeps the papers you read on arXiv, INSPIRE, NASA ADS and journal sites in one folder you choose.

Recruiting

I am currently accepting master's students.

  • I'm looking for students who can work hard with positive energy.
  • Passing the graduate entrance examination is the minimum requirement.
  • Details will be discussed in an interview.
Get in touch