OSHITA Naritaka

Department of ScienceLecturer

Last Updated :2026/08/04

■Researcher basic information

Homepage URL

Researcher number

50911632

ORCID ID

0000-0002-8799-1382

J-Global ID

Research Keyword

  • black holes   gravity   gravitational wave   cosmology   quantum field theory   

Research Field

  • Natural sciences / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

■Career

Career

  • 2026/04 - Today  Kindai UniversityFaculty of Science and Engineering Department of ScienceLecturer
  • 2023/05 - Today  RIKEN数理創造プログラム客員研究員
  • 2023/04 - 2026/03  京都大学 白眉センター特定助教
  • 2021/04 - 2023/03  RIKENInterdisciplinary Theoretical and Mathematical Sciences ProgramSpecial Postdoctoral Researcher
  • 2019/04 - 2021/03  Perimeter Institute for Theoretical PhysicsJSPS Fellow

Educational Background

  • 2014/04 - 2019/03  The University of Tokyo  Graduate School of Science  Department of Physics
  • 2011/04 - 2014/03  Hiroshima University  Faculty of Science  Physics

■Research activity information

Award

  • 2022/09 Scholarship of Particle Physics Nakamura Seitaro Prize
     On the study of black hole ringing 
    受賞者: Naritaka Oshita
  • 2019/03 The University of Tokyo School of Science Encouragement Award
     On the study of quantum black holes 
    受賞者: Naritaka Oshita

Paper

  • Nao Nakamoto; Naritaka Oshita
    Physical Review D American Physical Society (APS) 113 (10) 2470-0010 2026/05
  • Hajime Kobayashi; Shinji Mukohyama; Naritaka Oshita; Kazufumi Takahashi; Vicharit Yingcharoenrat
    Physical Review D American Physical Society (APS) 113 (8) 2470-0010 2026/04
  • Daiki Watarai; Naritaka Oshita; Daichi Tsuna
    Physical Review D American Physical Society (APS) 113 (4) 2470-0010 2026/02
  • Hajime Kobayashi; Shinji Mukohyama; Naritaka Oshita; Kazufumi Takahashi; Vicharit Yingcharoenrat
    Physical Review D American Physical Society (APS) 112 (8) 2470-0010 2025/10
  • Shogo Tomizuka; Hajime Kobayashi; Naritaka Oshita; Kazufumi Takahashi; Shinji Mukohyama
    Journal of Cosmology and Astroparticle Physics IOP Publishing 2025 (10) 056 - 056 2025/10 
    Abstract We study the dynamics of odd-parity perturbations on a static and spherically symmetric black hole background with a timelike vector field based on the effective field theory (EFT) approach.We derive the quadratic Lagrangian written in terms of two master variables, corresponding to the tensor and vector gravitons, which are coupled in general, while they can be decoupled on a stealth Schwarzschild(-de Sitter) background. For the stealth Schwarzschild background, we find that the quasinormal mode frequencies for both degrees of freedom are obtained from those in general relativity by simple scaling. Nonetheless, due to the fact that the metric perturbation is a non-trivial linear combination of the two degrees of freedom with different QNM spectra, the ringdown gravitational waves may exhibit characteristic modulation that can in principle be a signature of vector-tensor gravity.
  • Naritaka Oshita; Emanuele Berti; Vitor Cardoso
    Physical Review Letters American Physical Society (APS) 135 (3) 0031-9007 2025/07
  • Taiga Miyachi; Ryo Namba; Hidetoshi Omiya; Naritaka Oshita
    Physical Review D American Physical Society (APS) 111 (12) 2470-0010 2025/06 
    We investigate black hole quasinormal modes using the exact Wentzel–Kramers–Brillouin (WKB) method. We perform an analytic continuation from the horizon to infinity along the positive real axis of the radial coordinate and impose appropriate boundary conditions at these asymptotic positions. We clarify the role of previously overlooked logarithmic spirals of Stokes curves and branch cuts emerging from the horizon. We carefully reformulate the derivation of the quasinormal mode conditions using the exact WKB analysis, incorporating the contributions from these features into the calculation. We successfully derive correct results for both solvable model examples and the Schwarzschild spacetime. Our formulation enjoys straightforward extensions to other background geometries as well as a wide range of other physical systems.
  • Naritaka Oshita; Vitor Cardoso
    Physical Review D American Physical Society (APS) 111 (10) 2470-0010 2025/05 
    In black hole perturbation formalism, the gravitational waveform is obtained by the convolution of the Green's function and the source term causing radiation emission. Hence, the ringdown properties, namely its start time, depend on both functions. The unknown time-shift encoded in the Green's function introduces a "time-shift problem" for ringdown. We study the ringdown time-shift problem by reconstructing a waveform via the excitation factors of quasi-normal modes (QNMs) of a spinning black hole. For the first time, we reconstruct ringdown with a significant number of QNMs weighted with their excitation factors and confirm its excellent convergence. We then precisely identify the ringdown starting time. We also find (i) that for moderate or large spins and $\ell=m=2$, QNMs should be included up to around the $20$th prograde overtones and around fifth retrograde overtones to reconstruct the ringdown waveform for the delta-function source with a mismatch threshold $ M < O(10^{-3})$. For higher angular modes, a more significant number of QNMs are necessary to reconstruct it; (ii) that the time shift of ringdown caused by the Green's function is the same for different $(\ell, m, n)$ modes but that nontrivial sources can change this conclusion. Finally, we demonstrate (iii) that the greybody factor can be reconstructed with the superposed QNM spectrum in the frequency domain.
  • Matthew Giesler; Sizheng Ma; Keefe Mitman; Naritaka Oshita; Saul A. Teukolsky; Michael Boyle; Nils Deppe; Lawrence E. Kidder; Jordan Moxon; Kyle C. Nelli; Harald P. Pfeiffer; Mark A. Scheel; William Throwe; Nils L. Vu
    Physical Review D American Physical Society (APS) 111 (8) 2470-0010 2025/04 
    Using high-accuracy numerical relativity waveforms, we confirm the presence of numerous overtones of the $\ell=2$, $m=2$ quasinormal mode early in the ringdown of binary black hole mergers. We do this by demonstrating the stability of the mode amplitudes at different fit times, ruling out the possibility that a linear superposition of modes unphysically fits a highly nonlinear part of the waveform. We also find a number of previously unidentified subdominant second-order quasinormal modes in the $(2,2)$ mode. Even though these modes are mathematically nonlinear, they nevertheless confirm the validity of perturbation theory as a good approximation for describing much of the ringdown.
  • Daiki Saito; Naritaka Oshita
    Journal of High Energy Physics Springer Science and Business Media LLC 2025 (2) 2025/02 
    Abstract The Hawking-Moss (HM) bounce solution implies that the tunneling amplitude between vacua is uniquely determined by the vacuum energy at the initial vacuum and the top of a potential barrier, regardless of the field distance between them ∆ϕ. This implausible conclusion was carefully discussed in [E. J. Weinberg, Phys. Rev. Lett. 98, 251303, (2007)], and it was concluded that the conventional HM amplitude is not reliable for a transition to the top of distant local maxima (hereinafter referred to as the remote HM transition). We revisit this issue and study the impact of the quantum tunneling effect on the remote HM transition. We demonstrate that the amplitude for such a distant transition is indeed smaller than the conventional HM amplitude by employing the Lorentzian path integral in a simple setup. We consider a linear potential, which allows for analytic treatments, and evaluate the up-tunneling probability of a homogeneous scalar field in de Sitter spacetime. The Picard-Lefschetz theory is employed to identify the relevant Lefschetz thimble, representing the relevant tunneling trajectory. We then compare the resulting transition amplitude with the conventional HM amplitude. We find that when the field separation |∆ϕ| is larger, the quantum-tunneling amplitude, estimated by our Lorentzian path integral, is smaller than that of the conventional HM amplitude. This implies that the transition amplitude may be significantly suppressed if the thermal interpretation is not applicable and the quantum-tunneling effect is dominant for the remote HM transition.
  • Masahide Yamaguchi; Naritaka Oshita; Yutaro Shoji
    Springer Proceedings in Physics Springer Nature Singapore 1 - 6 0930-8989 2025
  • Naritaka Oshita; Kazufumi Takahashi; Shinji Mukohyama
    Physical Review D American Physical Society (APS) 110 (8) 2470-0010 2024/10 
    Recently, it has been proposed that the black hole greybody factors can be important to model ringdown spectral amplitudes. We study the stability of greybody factors against a small-bump correction in the perturbation equation. We find (I) that the greybody factor is stable in the frequency region relevant to ringdown and (II) that it is destabilized at higher frequencies, especially for a sharper bump correction. This behavior is similar to the case of higher overtones, which is also very sensitive to a small correction. We clarify this (in)stability with the WKB analysis. As the greybody factor is stable at the frequency region relevant to the main part of ringdown, we conclude that the greybody factor is suitable to model ringdown amplitude. In order to investigate a bump correction in a self-consistent manner, we consider the small-bump correction that can be realized in the general framework of effective field theory of black hole perturbations.
  • Etera R. Livine; Clara Montagnon; Naritaka Oshita; Hugo Roussille
    Journal of Cosmology and Astroparticle Physics IOP Publishing 2024 (10) 037 - 037 2024/10 
    Abstract We compute the Quasi-Normal Mode (QNM) frequencies for scalar perturbations for modified Schwarzschild black holes in Loop Quantum Gravity. We study the singularity-free polymerized metric characterized by two parameters encoding loop quantum effects: the minimal area gapa0and the polymeric deformation parameterP. We perform numerical computations using Leaver's continued fraction method and compare our results to other semi-analytical methods and existing literature. We study the effects on the QNM spectrum of variation of both deformation parameters and systematically compare to the standard Schwarzschild case. In particular we find that the scalar fundamental mode is modified from the third decimal for values ofPin accordance with the most recent astrophysical constraints. We also show that qualitative differences arise for highly damped modes: on the one hand, a new crossing of the imaginary axis occurs for high values ofa0and, on the other hand, increasingPproduces a positive shift of the real part and an increase of the spacing in imaginary part between modes.
  • Kazumasa Okabayashi; Naritaka Oshita
    Physical Review D American Physical Society (APS) 110 (6) 2470-0010 2024/09
  • Chams Gharib Ali Barura; Hajime Kobayashi; Shinji Mukohyama; Naritaka Oshita; Kazufumi Takahashi; Vicharit Yingcharoenrat
    Journal of Cosmology and Astroparticle Physics IOP Publishing 2024 (09) 001 - 001 2024/09 
    Abstract We study static tidal Love numbers (TLNs) of a static and spherically symmetric black hole for odd-parity metric perturbations.We describe black hole perturbations using the effective field theory (EFT), formulated on an arbitrary background with a timelike scalar profile in the context of scalar-tensor theories.In particular, we obtain a static solution for the generalized Regge-Wheeler equation order by order in a modified-gravity parameter and extract the TLNs uniquely by analytic continuation of the multipole index ℓ to non-integer values.For a stealth Schwarzschild black hole, the TLNs are vanishing as in the case of Schwarzschild solution in general relativity.We also study the case of Hayward black hole as an example of non-stealth background, where we find that the TLNs are non-zero (or there is a logarithmic running).This result suggests that our EFT allows for non-vanishing TLNs and can in principle leave a detectable imprint on gravitational waves from inspiralling binary systems, which opens a new window for testing gravity in the strong-field regime.
  • Vitor Cardoso; Shinji Mukohyama; Naritaka Oshita; Kazufumi Takahashi
    Physical Review D American Physical Society (APS) 109 (12) 2470-0010 2024/06 
    The Standard Model of particle physics predicts the speed of light to be a universal speed of propagation of massless carriers. However, other possibilities exist -- including Lorentz-violating theories -- where different fundamental fields travel at different speeds. Black holes are interesting probes of such physics, as distinct fields would probe different horizons. Here, we build an exact spacetime for two interacting scalar fields which have different propagation speeds. One of these fields is able to probe the black hole interior of the other, giving rise to energy extraction from the black hole and a characteristic late-time relaxation. Our results provide further stimulus to the search for extra degrees of freedom, black hole instability, and extra ringdown modes in gravitational-wave events.
  • Naritaka Oshita
    Physical Review D American Physical Society (APS) 109 (10) 2470-0010 2024/05
  • Naritaka Oshita; Yutaro Shoji; Masahide Yamaguchi
    Progress of Theoretical and Experimental Physics Oxford University Press (OUP) 2024 (6) 2024/05 
    Abstract We use the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to find the least bounce action in an AdS false vacuum state, i.e. the most probable decay process of the metastable AdS vacuum within the Euclidean formalism by Callan and Coleman. It was shown that the O(4) symmetric bounce solution leads to the action minimum in the absence of gravity, but it is nontrivial in the presence of gravity. The AdS/CFT duality is used to evade the difficulties particular to a metastable gravitational system. To this end, we show that the Fubini bounce solution in CFT, corresponding to the Coleman–de Luccia (CdL) bounce in AdS, gives the least action among all finite bounce solutions in a conformal scalar field theory. Thus, we prove that the CdL action is the least action among all possible large and thin-wall configurations under certain conditions.
  • Naritaka Oshita; Daichi Tsuna
    Physical Review D American Physical Society (APS) 108 (10) 2470-0010 2023/11
  • LISA Consortium Waveform Working Group; Niayesh Afshordi; Sarp Akçay; Pau Amaro Seoane; Andrea Antonelli; Josu C. Aurrekoetxea; Leor Barack; Enrico Barausse; Robert Benkel; Laura Bernard; Sebastiano Bernuzzi; Emanuele Berti; Matteo Bonetti; Béatrice Bonga; Gabriele Bozzola; Richard Brito; Alessandra Buonanno; Alejandro Cárdenas-Avendaño; Marc Casals; David F. Chernoff; Alvin J. K. Chua; Katy Clough; Marta Colleoni; Mekhi Dhesi; Adrien Druart; Leanne Durkan; Guillaume Faye; Deborah Ferguson; Scott E. Field; William E. Gabella; Juan García-Bellido; Miguel Gracia-Linares; Davide Gerosa; Stephen R. Green; Maria Haney; Mark Hannam; Anna Heffernan; Tanja Hinderer; Thomas Helfer; Scott A. Hughes; Sascha Husa; Soichiro Isoyama; Michael L. Katz; Chris Kavanagh; Gaurav Khanna; Larry E. Kidder; Valeriya Korol; Lorenzo Küchler; Pablo Laguna; François Larrouturou; Alexandre Le Tiec; Benjamin Leather; Eugene A. Lim; Hyun Lim; Tyson B. Littenberg; Oliver Long; Carlos O. Lousto; Geoffrey Lovelace; Georgios Lukes-Gerakopoulos; Philip Lynch; Rodrigo P. Macedo; Charalampos Markakis; Elisa Maggio; Ilya Mandel; Andrea Maselli; Josh Mathews; Pierre Mourier; David Neilsen; Alessandro Nagar; David A. Nichols; Jan Novák; Maria Okounkova; Richard O'Shaughnessy; Naritaka Oshita; Conor O'Toole; Zhen Pan; Paolo Pani; George Pappas; Vasileios Paschalidis; Harald P. Pfeiffer; Lorenzo Pompili; Adam Pound; Geraint Pratten; Hannes R. Rüter; Milton Ruiz; Zeyd Sam; Laura Sberna; Stuart L. Shapiro; Deirdre M. Shoemaker; Carlos F. Sopuerta; Andrew Spiers; Hari Sundar; Nicola Tamanini; Jonathan E. Thompson; Alexandre Toubiana; Antonios Tsokaros; Samuel D. Upton; Maarten van de Meent; Daniele Vernieri; Jeremy M. Wachter; Niels Warburton; Barry Wardell; Helvi Witek; Vojtěch Witzany; Huan Yang; Miguel Zilhão; Angelica Albertini; K. G. Arun; Miguel Bezares; Alexander Bonilla; Christian Chapman-Bird; Bradley Cownden; Kevin Cunningham; Chris Devitt; Sam Dolan; Francisco Duque; Conor Dyson; Chris L. Fryer; Jonathan R. Gair; Bruno Giacomazzo; Priti Gupta; Wen-Biao Han; Roland Haas; Eric W. Hirschmann; E. A. Huerta; Philippe Jetzer; Bernard Kelly; Mohammed Khalil; Jack Lewis; Nicole Lloyd-Ronning; Sylvain Marsat; Germano Nardini; Jakob Neef; Adrian Ottewill; Christiana Pantelidou; Gabriel Andres Piovano; Jaime Redondo-Yuste; Laura Sagunski; Leo C. Stein; Viktor Skoupý; Ulrich Sperhake; Lorenzo Speri; Thomas F. M. Spieksma; Chris Stevens; David Trestini; Alex Vañó-Viñuales
    2023/11 
    LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.
  • Naritaka Oshita; Niayesh Afshordi
    Physics Letters B Elsevier BV 841 137901 - 137901 0370-2693 2023/06 
    We estimate the canonical entropy of a quantum black hole by counting its quasi-normal modes. We first show that the partition function of a classical black hole, evaluated by counting the quasi-normal modes with a thermodyanmic Boltzmann weight, leads to a small entropy of order unity due to the small contribution from higher angular modes. We then discuss how this will be modified when taking into account dissipation effects near the horizon due to interaction with the quantum black hole microstates. The structure of quasi-normal modes drastically changes, yielding a fundamental frequency of the inverse of $t_{\rm echo} \sim$ log(Entropy)/Temperature. This is the time-scale for reflection from the microstates (or the quantum time limit of silence, followed by echoes), $\textit{independent of the strength of dissipation}$, and is comparable to the scrambling time proposed by Sekino & Susskind. Setting the dissipation constant to Planck time, we reproduce the Bekenstein-Hawking entropy of $\sim$ (Horizon area)/(Planck area). This result suggests the possibility of simulating black hole entropy in analog horizons realized in condensed matter systems.
  • Issei Koga; Naritaka Oshita; Kazushige Ueda
    Journal of High Energy Physics Springer Science and Business Media LLC 2023 (5) 2023/05 
    Abstract The emergence of a four-dimensional de Sitter (dS4) universe on an expanding bubble in the five-dimensional anti-de Sitter (AdS5) background has been suggested as a possible cosmological scenario. It is motivated by the difficulties in the realization of a stable de Sitter vacua in string theory. The bubble can be nucleated in a meta-stable pure AdS5 spacetime, but it is known that a pure AdS spacetime is non-perturbatively unstable. It means that the pure AdS5 background is an idealized situation, and in realistic situations, non-linear perturbations in AdS may lead to the formation of black holes due to the gravitational turbulent instability. To investigate how the proposed scenario works in a more realistic situation, we here study the nucleation process of a vacuum bubble in the Kerr-AdS5 spacetime. Especially we investigate conditions sufficient to ensure the nucleation of a vacuum bubble with a rotating black hole and how the black hole affects the transition rate. We find that even in the Kerr-AdS5 spacetime, a quasi-dS4 expansion can be realized on the nucleated vacuum bubble without contradicting the de Sitter swampland conjectures.
  • Naritaka Oshita
    Journal of Cosmology and Astroparticle Physics IOP Publishing 2023 (04) 013 - 013 2023/04 
    Abstract We find a significant destructive interference among Kerr overtones in the early ringdown induced by an extreme mass-ratio merger of a massive black hole and a compact object, and that the ringdown spectrum apparently follows the Fermi-Dirac distribution. We numerically compute the spectral amplitude of gravitational waves induced by a particle plunging into a Kerr black hole and study the excitation of multiple quasi-normal (QN) modes. We find that the start time of ringdown is before the strain peak of the signal and corresponds to the time when the particle passes the photon sphere. When the black hole has the near-extremal rotation, the Kerr QN frequencies are close to the fermionic Matsubara frequencies with the Hawking temperature and the chemical potential of the superradiant frequency. We indeed find that the absolute square of the spectral amplitude apparently follows the Fermi-Dirac distribution with the chemical potential of around the real QN frequency of the fundamental mode. Fitting the Boltzmann distribution to the data in higher frequencies, the best-fit temperature is found out to be close to the Hawking temperature, especially for rapid rotations. In the near-extremal limit, the gravitational-wave spectrum exhibits a would-be Fermi degeneracy with the Fermi surface at the superradiant frequency ω = μH. We show that the greybody factor, i.e., the absorption cross section of a black hole, leads to the Fermi-Dirac distribution. As the greybody factor is another no-hair quantity of black holes, this opens a new possibility that we could test general relativity by observationally searching for the Boltzmann distribution in ringdown, provided that near-extremal black holes exist in the observable region. Indeed, it has been predicted that near-extremal supermassive black holes would exist at the center of some galaxies from the X-ray reflection spectroscopy. We could measure the mass and angular momentum of ringing black holes and could probe the Kerr/CFT correspondence by measuring the greybody factor imprinted on the ringdown spectrum.
  • Naritaka Oshita; Yutaro Shoji; Masahide Yamaguchi
    Physical Review D American Physical Society (APS) 107 (4) 2470-0010 2023/02
  • Naritaka Oshita; Hayato Motohashi; Sousuke Noda
    PHYSICAL REVIEW D 106 (4) 2470-0010 2022/08
  • Issei Koga; Naritaka Oshita; Kazushige Ueda
    PHYSICAL REVIEW D 105 (12) 2470-0010 2022/06
  • Takumi Hayashi; Kohei Kamada; Naritaka Oshita; Jun'ichi Yokoyama
    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (5) 1475-7516 2022/05
  • Naritaka Oshita
    PHYSICAL REVIEW D 104 (12) 2470-0010 2021/12
  • Ruth Gregory; Ian G. Moss; Naritaka Oshita; Sam Patrick
    CLASSICAL AND QUANTUM GRAVITY 38 (18) 0264-9381 2021/09
  • Naritaka Oshita; Niayesh Afshordi; Shinji Mukohyama
    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (5) 1475-7516 2021/05
  • Naritaka Oshita; Kazushige Ueda; Masahide Yamaguchi
    Journal of High Energy Physics Springer Science and Business Media Deutschland GmbH 2020 (10) 1029-8479 2020/10
  • Naritaka Oshita; Kazushige Ueda; Masahide Yamaguchi
    JOURNAL OF HIGH ENERGY PHYSICS (10) 1029-8479 2020/10
  • Ruth Gregory; Ian G. Moss; Naritaka Oshita; Sam Patrick
    JOURNAL OF HIGH ENERGY PHYSICS (9) 1029-8479 2020/09
  • Takumi Hayashi; Kohei Kamada; Naritaka Oshita; Jun'ichi Yokoyama
    JOURNAL OF HIGH ENERGY PHYSICS (8) 1029-8479 2020/08
  • Ruth Gregory; Ian G. Moss; Naritaka Oshita
    JOURNAL OF HIGH ENERGY PHYSICS (7) 1029-8479 2020/07
  • Naritaka Oshita; Daichi Tsuna; Niayesh Afshordi
    PHYSICAL REVIEW D 102 (2) 1550-7998 2020/07
  • Naritaka Oshita; Daichi Tsuna; Niayesh Afshordi
    PHYSICAL REVIEW D 102 (2) 1550-7998 2020/07
  • Naritaka Oshita
    CLASSICAL AND QUANTUM GRAVITY 37 (7) 0264-9381 2020/04
  • Naritaka Oshita; Qingwen Wang; Niayesh Afshordi
    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS (4) 1475-7516 2020/04
  • Jahed Abedi; Niayesh Afshordi; Naritaka Oshita; Qingwen Wang
    UNIVERSE 6 (3) 2020/03
  • Barausse, E.; Berti, E.; Hertog, T.; Hughes, S.A.; Jetzer, P.; Pani, P.; Sotiriou, T.P.; Tamanini, N.; Witek, H.; Yagi, K.; Yunes, N.; Abdelsalhin, T.; Achucarro, A.; van Aelst, K.; Afshordi, N.; Akcay, S.; Annulli, L.; Arun, K.G.; Ayuso, I.; Baibhav, V.; Baker, T.; Bantilan, H.; Barreiro, T.; Barrera-Hinojosa, C.; Bartolo, N.; Baumann, D.; Belgacem, E.; Bellini, E.; Bellomo, N.; Ben-Dayan, I.; Bena, I.; Benkel, R.; Bergshoefs, E.; Bernard, L.; Bernuzzi, S.; Bertacca, D.; Besancon, M.; Beutler, F.; Beyer, F.; Bhagwat, S.; Bicak, J.; Biondini, S.; Bize, S.; Blas, D.; Boehmer, C.; Boller, K.; Bonga, B.; Bonvin, C.; Bosso, P.; Bozzola, G.; Brax, P.; Breitbach, M.; Brito, R.; Bruni, M.; Br{\"u}gmann, B.; Bulten, H.; Buonanno, A.; Burko, L.M.; Burrage, C.; Cabral, F.; Calcagni, G.; Caprini, C.; C{\'a}rdenas-Avenda{\~n}o, A.; Celoria, M.; Chatziioannou, K.; Chernoff, D.; Clough, K.; Coates, A.; Comelli, D.; Comp{\`e}re, G.; Croon, D.; Cruces, D.; Cusin, G.; Dalang, C.; Danielsson, U.; Das, S.; Datta, S.; de Boer, J.; De Luca, V.; De Rham, C.; Desjacques, V.; Destounis, K.; Filippo, F.D.; Dima, A.; Dimastrogiovanni, E.; Dolan, S.; Doneva, D.; Duque, F.; Durrer, R.; East, W.; Easther, R.; Elley, M.; Ellis, J.R.; Emparan, R.; Ezquiaga, J.M.; Fairbairn, M.; Fairhurst, S.; Farmer, H.F.; Fasiello, M.R.; Ferrari, V.; Ferreira, P.G.; Ficarra, G.; Figueras, P.; Fisenko, S.; Foffa, S.; Franchini, N.; Franciolini, G.; Fransen, K.; Frauendiener, J.; Frusciante, N.; Fujita, R.; Gair, J.; Ganz, A.; Garcia, P.; Garcia-Bellido, J.; Garriga, J.; Geiger, R.; Geng, C.; Gergely, L.?; Germani, C.; Gerosa, D.; Giddings, S.B.; Gourgoulhon, E.; Grandclement, P.; Graziani, L.; Gualtieri, L.; Haggard, D.; Haino, S.; Halburd, R.; Han, W.-B.; Hawken, A.J.; Hees, A.; Heng, I.S.; Hennig, J.; Herdeiro, C.; Hervik, S.; Holten, J.; Hoyle, C.J.D.; Hu, Y.; Hull, M.; Ikeda, T.; Isi, M.; Jenkins, A.; Juli{\'e}, F.; Kajfasz, E.; Kalaghatgi, C.; Kaloper, N.; Kamionkowski, M.; Karas, V.; Kastha, S.; Keresztes, Z.; Kidder, L.; Kimpson, T.; Klein, A.; Klioner, S.; Kokkotas, K.; Kolesova, H.; Kolkowitz, S.; Kopp, J.; Koyama, K.; Krishnendu, N.V.; Kroon, J.A.V.; Kunz, M.; Lahav; O. and; dragin, A.; Lang, R.N.; Poncin-Lafitte, C.L.; Lemos, J.; Li, B.; Liberati, S.; Liguori, M.; Lin, F.; Liu, G.; Lobo; F.S.N.; Loll, R.; Lombriser, L.; Lovelace, G.; Macedo, R.P.; Madge, E.; Maggio, E.; Maggiore, M.; Marassi, S.; Marcoccia, P.; Markakis, C.; Martens, W.; Martinovic, K.; Martins, C.J.A.P.; Maselli, A.; Mastrogiovanni, S.; Matarrese, S.; Matas, A.; Mavromatos, N.E.; Mazumdar, A.; Meerburg, P.D.; Megias, E.; Miller, J.; Mimoso, J.P.; Mittnacht, L.; Montero, M.M.; Moore, B.; Martin-Moruno, P.; Musco, I.; Nakano, H.; Nampalliwar, S.; Nardini, G.; Nielsen, A.; Nov{\'a}k, J.; Nunes, N.J.; Okounkova, M.; Oliveri, R.; Oppizzi, F.; Orlando, G.; Oshita, N.; Pappas, G.; Paschalidis, V.; Peiris, H.; Peloso, M.; Perkins, S.; Pettorino, V.; Pikovski, I.; Pilo, L.; Podolsky, J.; Pontzen, A.; Prabhat, S.; Pratten, G.; Prokopec, T.; Prouza, M.; Qi, H.; Raccanelli, A.; Rajantie, A.; Randall, L.; Raposo, G.; Raymond, V.; Renaux-Petel, S.; Ricciardone, A.; Riotto, A.; Robson, T.; Roest, D.; Rollo, R.; Rosofsky, S.; Ruan, J.J.; Rubiera-Garc{\'i}a, D.; Ruiz, M.; Rusu, M.; Sabatie, F.; Sago, N.; Sakellariadou, M.; Saltas, I.D.; Sberna, L.; Sathyaprakash, B.; Scheel, M.; Schmidt, P.; Schutz, B.; Schwaller, P.; Shao, L.; Shapiro, S.L.; Shoemaker, D.; Silva, A.; Simpson, C.; Sopuerta, C.F.; Spallicci, A.; Stefanek, B.A.; Stein, L.; Stergioulas, N.; Stott, M.; Sutton, P.; Svarc, R.; Tagoshi, H.; Tahamtan, T.; Takeda, H.; Tanaka, T.; Tantilian, G.; Tasinato, G.; Tattersall, O.; Teukolsky, S.; Tiec, A.L.; Theureau, G.; Trodden, M.; Tolley, A.; Toubiana, A.; Traykova, D.; Tsokaros, A.; Unal, C.; Unnikrishnan, C.S.; Vagenas, E.C.; Valageas, P.; Vallisneri, M.; Brand, J.V.; Broeck, C.V.; de Meent, M.; Vanhove, P.; Varma, V.; Veitch, J.; Vercnocke, B.; Verde, L.; Vernieri, D.; Vernizzi, F.; Vicente, R.; Vidotto, F.; Visser, M.; Vlah, Z.; Vretinaris, S.; V{\"o}lkel, S.; Wang, Q.; Wang, Y.-T.; Werner, M.C.; Westernacher, J.; Weygaert, R.; Wiltshire, D.; Wiseman, T.; Wolf, P.; Wu, K.; Yamada, K.; Yang, H.; Yi, L.; Yue, X.; Yvon, D.; Zilh{\~a}o, M.; Zimmerman, A.; Zumalacarregui, M.
    General Relativity and Gravitation 52 (8) 1572-9532 2020
  • Naritaka Oshita; Kazushige Ueda; Masahide Yamaguchi
    JOURNAL OF HIGH ENERGY PHYSICS (1) 1029-8479 2020/01
  • Qingwen Wang; Naritaka Oshita; Niayesh Afshordi
    PHYSICAL REVIEW D 101 (2) 2470-0010 2020/01
  • Naritaka Oshita; Masaki Yamada; Masahide Yamaguchi
    PHYSICS LETTERS B 791 149 - 155 0370-2693 2019/04
  • Naritaka Oshita; Niayesh Afshordi
    PHYSICAL REVIEW D 99 (4) 2470-0010 2019/02
  • Naritaka Oshita; Jun'ichi Yokoyama
    INTERNATIONAL JOURNAL OF MODERN PHYSICS A 33 (31) 0217-751X 2018/11
  • Naritaka Oshita; Jun'ichi Yokoyama
    PHYSICS LETTERS B 785 197 - 200 0370-2693 2018/10
  • Naritaka Oshita
    PHYSICAL REVIEW D 97 (2) 2470-0010 2018/01
  • Naritaka Oshita
    CLASSICAL AND QUANTUM GRAVITY 34 (19) 0264-9381 2017/10
  • Naritaka Oshita; Yi-Peng Wu
    PHYSICAL REVIEW D 96 (4) 2470-0010 2017/08
  • Naritaka Oshita; Kazuhiro Yamamoto; Sen Zhang
    Everything about Gravity, Proceedings of the Second LeCosPA International Symposium 31 March 2017 584 - 589 2017/03
  • Satoshi Iso; Naritaka Oshita; Rumi Tatsukawa; Kazuhiro Yamamoto; Sen Zhang
    PHYSICAL REVIEW D 95 (2) 2470-0010 2017/01
  • Naritaka Oshita; Jun'ichi Yokoyama
    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 2016 (5) 2050-3911 2016/05
  • Naritaka Oshita; Kazuhiro Yamamoto; Sen Zhang
    PHYSICAL REVIEW D 93 (8) 2470-0010 2016/04
  • Naritaka Oshita; Kazuhiro Yamamoto; Sen Zhang
    PHYSICAL REVIEW D 92 (4) 1550-7998 2015/08
  • Naritaka Oshita; Jun'ichi Yokoyama
    Proceedings of the 25th Workshop on General Relativity and Gravitation in Japan, JGRG 2015 2 376 - 382 2015
  • Naritaka Oshita; Kazuhiro Yamamoto; Sen Zhang
    Proceedings of the 25th Workshop on General Relativity and Gravitation in Japan, JGRG 2015 5 1385 - 1396 2015
  • Naritaka Oshita; Kazuhiro Yamamoto; Sen Zhang
    PHYSICAL REVIEW D 89 (12) 1550-7998 2014/06

Affiliated academic society

  • Japan Society of Physics   

Research Themes

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2026/03 
    Author : 大下 翔誉
     
    主な研究実績は、リングダウン重力波の振幅の新たなモデル化の手法を提案したことである。従来までは、リングダウン重力波波形は、複数の準固有振動の重ね合わせでモデル化することが一般的であった。しかしこれには、複数のフィッティングパラメーターが必要で、「オーバーフィッティング」というデータ解析上の問題を引き起こすことが知られている。しかし今回提唱した新たなモデルでは、準固有振動ではなく、ブラックホール周りに在るlight ringの透過率を表すgreybody因子でリングダウン重力波の振幅をモデルする。これを用いる利点として、フィッティングパラメーターの数が極めて少なくなること、そしてリングダウン重力波放射の開始開始時刻の不定性がないことが挙げられる。 当該年度で発表した研究成果の１つでは、このgreybody因子によるリングダウン重力波のモデルが、少なくとも質量比が極めて大きいブラックホール合体の場合に適用可能であることを指摘した。 この他にも、高速自転する超大質量ブラックホールを起源とするリングダウン重力波には、長寿命な準固有振動が複数含まれていることから、重力理論の検証において極めて有利となることを研究で明らかにした。LISAによる将来観測を想定し、フィッシャー解析に基づいて準固有振動数の検出精度を精細に調べた。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2021/08 -2023/03 
    Author : 大下 翔誉
     
    これまでの主な研究実績として、(1)ローレンツ経路積分に基づいた真空崩壊の新たな定式化や、(2)Wheeler-deWitt形式に基づいた真空崩壊の定式化が挙げられる。 これまで真空崩壊は定常的な時空の上で虚時間を導入するユークリッド経路積分に基づいていた。より現実的な系で真空崩壊を記述するには、ユークリッド経路積分による定式化を超えることが重要である。(1)では、まず簡易的な系での計算を実行するために、重力が存在しない系かつ真空泡の構造が薄い球殻の運動で記述できる場合を想定し、その真空泡の生成率をローレンツ経路積分で評価した。この経路積分の計算には、Picard-Lefschetz理論を適用した。その結果、ユークリッド経路積分の結果を再現することを見出した。これは、ローレンツ経路積分が真空崩壊の定式化として機能することを示した意義深い例である。 従来の計算法では、量子トンネリングを起こしている領域と起こしていない領域の両方に虚時間を導入し、真空泡の構造を与える解を計算していた。しかし実際にはトンネリングを起こす領域は局所的であり、この描像を反映した定式化を導入することで、新たな真空泡の構造が見える可能性がある。そこで(2)では、真空崩壊により量子トンネリングを経験する領域とそうでない領域をそれぞれ、ユークリッド描像とローレンツ描像で局所的に記述するため、時空を量子的に扱うことを目的としたWheeler-DeWitt形式に基づいて、真空崩壊の計算を試みた。その結果、これまで知られていたColeman-de Luccia解よりも高い相転移確率を有する解を数値的に見出した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2019/03 
    Author : 大下 翔誉
     
    重力場における量子論は、統一理論の構築のみならず、宇宙の起源や星の重力崩壊の解明においても極めて重要な役割を担うと考えられている。前年度までは、基礎的な問題として、曲がった時空での場の量子論の解明のために、Unruh効果という加速度系における粒子生成の理論的研究を行ない、その検証可能性まで議論を行ってきた。当該年度においては、強重力場における量子論の検証可能性に対して、重力波の観点からアプローチした。近年検出されたブラックホール連星合体からの重力波によって、量子重力の性質を知ることができるかを理論的に調べたのである。ブラックホール連星合体からの重力波の中でも、特にリングダウン重力波という「ブラックホール合体の十分後に緩和過程として現れる重力波」に注目した。そのリングダウン重力波には、ブラックホールの質量、角運動量とブラックホール地平面付近の境界条件だけで決まる固有振動数のみが含まれている。したがって、もし量子論的な効果で境界条件が修正を受けている場合、ブラックホールの固有振動数、つまりリングダウン重力波に影響が及んでいる可能性があるため、このリングダウン重力波の精細な観測には重要な意義がある。量子重力が効いてくるエネルギースケールで重力波の分散関係がずれている場合に、それがブラックホール合体からの重力波に無視できない規模で影響を及ぼすことを明らかにした。今後、重力波観測は益々精度を上げていくことが期待される。それとともに天体物理だけでなく、ブラックホールの量子論的な性質にも迫れる可能性を示唆したという意味で、本研究は極めて意義深いものである。