Hirotada Okawa
Waseda University
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Publication
Featured researches published by Hirotada Okawa.
Classical and Quantum Gravity | 2015
Emanuele Berti; Enrico Barausse; Vitor Cardoso; Leonardo Gualtieri; Paolo Pani; Ulrich Sperhake; Leo C. Stein; Norbert Wex; Kent Yagi; Tessa Baker; C. P. Burgess; Flávio S. Coelho; Daniela D. Doneva; Antonio De Felice; Pedro G. Ferreira; P. C. C. Freire; James Healy; Carlos Herdeiro; Michael Horbatsch; Burkhard Kleihaus; Antoine Klein; Kostas D. Kokkotas; Jutta Kunz; Pablo Laguna; Ryan N. Lang; Tjonnie G. F. Li; T. B. Littenberg; Andrew Matas; Saeed Mirshekari; Hirotada Okawa
One century after its formulation, Einsteins general relativity (GR) has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in the weak-field regime, and there are theoretical and experimental reasons to believe that GR should be modified when gravitational fields are strong and spacetime curvature is large. The best astrophysical laboratories to probe strong-field gravity are black holes and neutron stars, whether isolated or in binary systems. We review the motivations to consider extensions of GR. We present a (necessarily incomplete) catalog of modified theories of gravity for which strong-field predictions have been computed and contrasted to Einsteins theory, and we summarize our current understanding of the structure and dynamics of compact objects in these theories. We discuss current bounds on modified gravity from binary pulsar and cosmological observations, and we highlight the potential of future gravitational wave measurements to inform us on the behavior of gravity in the strong-field regime.
Physical Review D | 2013
Kenta Hotokezaka; Kenta Kiuchi; Koutarou Kyutoku; Hirotada Okawa; Yuichiro Sekiguchi; Masaru Shibata; Keisuke Taniguchi
Numerical-relativity simulations for the merger of binary neutron stars are performed for a variety of equations of state (EOSs) and for a plausible range of the neutron-star mass, focusing primarily on the properties of the material ejected from the system. We find that a fraction of the material is ejected as a mildly relativistic and mildly anisotropic outflow with the typical and maximum velocities
Physical Review D | 2011
Kenta Hotokezaka; Koutarou Kyutoku; Hirotada Okawa; Masaru Shibata; Kenta Kiuchi
\sim 0.15
Physical Review D | 2015
Koutarou Kyutoku; Kunihito Ioka; Hirotada Okawa; Masaru Shibata; Keisuke Taniguchi
--
Classical and Quantum Gravity | 2012
Vitor Cardoso; Leonardo Gualtieri; Carlos Herdeiro; Ulrich Sperhake; Paul M. Chesler; Luis Lehner; S. Park; Harvey S. Reall; Carlos F. Sopuerta; Daniela Alic; Oscar J. C. Dias; Roberto Emparan; Valeria Ferrari; Steven B. Giddings; Mahdi Godazgar; Ruth Gregory; Veronika E. Hubeny; Akihiro Ishibashi; Greg Landsberg; Carlos O. Lousto; David Mateos; Vicki Moeller; Hirotada Okawa; Paolo Pani; M. Andy Parker; Frans Pretorius; Masaru Shibata; Hajime Sotani; Toby Wiseman; Helvi Witek
0.25c
Physical Review Letters | 2013
Chul-Moon Yoo; Hirotada Okawa; Ken-ichi Nakao
and
Physical Review D | 2011
Hirotada Okawa; Ken-ichi Nakao; Masaru Shibata
\sim 0.5
Physical Review D | 2014
Masaru Shibata; Keisuke Taniguchi; Hirotada Okawa; A. Buonanno
--
Physical Review D | 2015
Kyohei Kawaguchi; Koutarou Kyutoku; Hiroyuki Nakano; Hirotada Okawa; Masaru Shibata; Keisuke Taniguchi
0.8c
Physical Review D | 2014
Hirotada Okawa; Helvi Witek; Vitor Cardoso
(where
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