A5103129892- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Relativity and Gravitational Theory
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Dark Matter and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Computational Physics and Python Applications
- Solar and Space Plasma Dynamics
- Experimental and Theoretical Physics Studies
- Astrophysics and Cosmic Phenomena
- Scientific Research and Discoveries
- Astro and Planetary Science
- Noncommutative and Quantum Gravity Theories
- Particle physics theoretical and experimental studies
- Advanced Thermodynamics and Statistical Mechanics
- Statistical Mechanics and Entropy
- Algebraic and Geometric Analysis
- Economic theories and models
- Advanced Differential Geometry Research
- Complex Systems and Time Series Analysis
- Radio Astronomy Observations and Technology
- Mathematical Dynamics and Fractals
Waseda University
2009-2025
Kyoto University
1977-2025
Centre de Recherche en Astronomie Astrophysique et Géophysique
1995
The University of Western Australia
1995
The University of Tokyo
1988-1990
Fermi National Accelerator Laboratory
1988-1990
Tokyo University of Science
1988
Observatoire de Paris
1988
The Abdus Salam International Centre for Theoretical Physics (ICTP)
1986-1987
Scuola Internazionale Superiore di Studi Avanzati
1986
The objectives of the DECi-hertz Interferometer Gravitational Wave Observatory (DECIGO) are to open a new window observation for gravitational wave astronomy and obtain insight into significant areas science, such as verifying characterizing inflation, determining thermal history universe, dark energy, describing formation mechanism supermassive black holes in center galaxies, testing alternative theories gravity, seeking hole matter, understanding physics neutron stars searching planets...
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the future Japanese space gravitational antenna. It aims at detecting various kinds of waves between 1 mHz and 100 Hz frequently enough to open a new window observation for astronomy. The pre-conceptual design DECIGO consists three drag-free satellites, 1000 km apart from each other, whose relative displacements are measured by Fabry–Perot Michelson interferometer. We plan launch in 2024 after long intense development...
Extending the proof of cosmic no-hair theorem for Bianchi models in power-law inflation, authors prove a more general all 0<or= lambda < square root 2, where is coupling constant an exponential potential inflaton phi , exp(- kappa ). For any initially expanding Bianchi-type model except type IX, they find that isotropic inflationary solution unique attractor and anisotropies always enhance inflation. this conclusion also true, if initial ratio vacuum energy Lambda eff to maximum 3-curvature...
We show the universe may contain Schwarzschild wormholes by first order phase transition of a vacuum. This result enables us to estimate reasonable time for completion transition.
Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at detection primordial gravitational waves, which could be produced during inflationary period right after birth universe. There are many other scientific objectives DECIGO, including direct measurement acceleration expansion universe, and reliable accurate predictions timing locations neutron star/black hole binary coalescences....
The stability condition of (the four-dimensional Friedmann universe)*(a compact internal space) (F4*KD) is presented for a class higher-dimensional theories, in which the effective potential depends only on scale length space. Candelas-Weinberg model (i.e. one-loop quantum correction+a cosmological constant Lambda ), eleven-dimensional supergravity+ , Einstein-Yang-Mills theory and six-dimensional Einstein-Maxwell are classified into this class. It shown that F4*KD solution stable against...
It has been pointed out recently that wormholes and black holes are created by cosmological first-order phase transition of vacuum. In the present paper this creation mechanism is discussed precisely. particular, we investigate how bubbles nucleated in a trapped false vacuum (a region surrounded true vacuum) change holes. As result, it found that, due to bubble vacuum, wormhole collapses hole some case, while neither nor another case.
Assuming the action from string theory and taking into account dynamical freedom of a dilaton its coupling to matter fluid, we show that fundamental ‘constants’ in theories are independent ‘radius’ internal space. Since scalar related is coupled 4-dimensional gravity fluid same way as Jordan-Brans-Dicke with ω=−1, it must be massive can get mass easily through some symmetry breaking mechanism (e.g. SUSY due gluino condensation). Consequently, time variation constants too small observed.
We study the cosmology resulting from two coupled scalar fields, one which is either a new or chaotic-type inflaton and another has an exponentially decaying potential. Such potential may appear in conformally transformed frame of generalized Einstein theories such as Jordan-Brans-Dicke theory. The constraints necessary for successful inflation are examined. find conventional grand unified theory models SU(5) compatible with inflation, while restrictions on self-coupling constant...
Using a black hole (BH) perturbation approach, we numerically study gravitational waves from spinning particle of mass $\ensuremath{\mu}$ and spin $s$ on the equatorial plane plunging into Kerr BH $M$ $a.$ When take account $s,$ (a) motion changes due to coupling effects between orbital angular momentum ${L}_{z}$ $a,$ also (b) energy tensor linearized Einstein equations changes. We calculate total radiated energy, linear momentum, spectrum, waveform waves, find following features. (1) There...
A fully relativistic formulation for a motion of compressed shell in an expanding dust universe is given the approximation infinitesimally thin shell. Using equation obtained, expansion law mass surrounding spherical void discussed. The derived and its solutions are Newtonian approximation.
We investigate two Type-IIa minimally modified gravity theories, namely V $(\ensuremath{\varphi})$ Cold Dark Matter (VCDM) and Cuscuton theories. confirm that all acceptable solutions are always for VCDM theory. However, the inverse does not hold. find allows existence of exact general relativity (GR) with or without presence matter fields a cosmological constant. determine conditions such GR-VCDM in terms trace extrinsic curvature on which define On other hand, theory, we same set GR (such...
Fractal structures and non-Gaussian velocity distributions are characteristic properties commonly observed in virialized self-gravitating systems, such as galaxies interstellar molecular clouds. We study the origin of these using a one-dimensional ring model that we propose this paper. In simple model, N particles moving, on circular fixed three-dimensional space, with mutual interaction gravity. This is suitable for accurate symplectic integration method by which argue phase transition...
DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is the planned Japanese space gravitational antenna, aiming to detect waves from astrophysically and cosmologically significant sources mainly between 0.1 Hz 10 thus open a new window for astronomy universe. DECIGO will consist of three drag-free spacecraft, 1000 km apart each other, whose relative displacements are measured by differential Fabry-Perot interferometer. We plan launch in middle 2020s, after sequence two...
We study gravitational theories with a cosmological constant and the Gauss-Bonnet curvature squared term analyze possibility of de Sitter expanding spacetime internal space. find that there are two branches solutions: both space (1) positive (2) negative. From stability analysis, we show solution case is unstable, while in stable. Namely present system stable if extend our analysis to higher-order Lovelock terms. Although existence solutions very complicated highly depend on coupling...
We investigate thermodynamics of static and spherically symmetric black holes (BHs) in the Horndeski theories. Because presence higher-derivative interactions nonminimal derivative couplings scalar field, standard Wald entropy formula may not be directly applicable. Hence, following original formulation by Iyer Wald, we obtain differentials BH total mass system theories, which lead to first law via conservation Hamiltonian. Our covers case solutions with field those linearly time-dependent...
Wormholes solutions are discussed in a theory with antisymmetric 3-rank tensor field Hmu nu rho (axion) coupled to scalar fields. The authors also consider generalised gravity theory, which action is given by S= integral d4x square root -g(F( phi ,R)-1/2h( )( Del )2-g2 2), F( ,R) and h( ) being arbitrary functions of curvature R. Since it conformally equivalent the Einstein-Hilbert system field, can apply above discussion such theory. Most models (R2 model, Jordan-Brans-Dicke Zee's induced...
For pt.I see ibid., vol.3, p.233 (1986). In most higher-dimensional theories, the effective matter Lagrangian after compactification is described not only by radius of internal space but also a set scalar fields (e.g. dilaton). The author presents stability conditions for (the four-dimensional Friedmann universe (F4))*(a constant (K)) in above class. against non-linear (large) perturbations and attractor property F4*K solution are investigated order to explain why our present one. If local...
We discuss cosmology based on a Cuscuta-Galileon gravity theory, which preserves just two degrees of freedom. Although there exists no additional freedom, introduction potential scalar field changes the dynamics. The is completely determined by matter fields. Giving an exponential as example, we cosmological gravitational "constant" $G_{\rm F}$ appeared in effective Friedmann equation becomes time dependent. also present how to construct when know evolution Hubble parameter. When assume...
Combining Geroch's and the ADM formalisms, we give a new formalism for treating dynamical problems of space-time having rotational Killing vector. We have found that basic equations rotating system strongly resemble Einstein Maxwell non-rotating system.
Using the ADM formalism, we give a method of solving general relativistic collapse an axially symmetric star by numerical calculation. At t=O, solve constraint equations to determine initial data metric tensors and extrinsic curvatures under given angular momentum distribution baryon number distribution. An example is shown. later time evolution hydrodynamics are solved. The not solved but used see accuracy details techniques shown for spherically case.