A5102780081- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Particle physics theoretical and experimental studies
- Black Holes and Theoretical Physics
- Galaxies: Formation, Evolution, Phenomena
- Advanced Chemical Physics Studies
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Astrophysics and Cosmic Phenomena
- Neutrino Physics Research
- Solar and Space Plasma Dynamics
- Spectroscopy and Laser Applications
- Relativity and Gravitational Theory
- Computational Physics and Python Applications
- Spectroscopy and Quantum Chemical Studies
- Radio Astronomy Observations and Technology
- Astronomy and Astrophysical Research
- Atmospheric Ozone and Climate
- Stellar, planetary, and galactic studies
- Photochemistry and Electron Transfer Studies
- Molecular Spectroscopy and Structure
- Atomic and Subatomic Physics Research
- Laser-Matter Interactions and Applications
- Astrophysics and Star Formation Studies
- Astrophysical Phenomena and Observations
Hokkaido University
1991-2025
The University of Tokyo
2015-2024
Kavli Institute for the Physics and Mathematics of the Universe
2014-2024
Hitachi (Japan)
2014-2019
Hitachi Global Storage Technologies (United States)
2019
University of Tsukuba
2018
Universidad de Zaragoza
2016
European Organization for Nuclear Research
2015
Research Institute for Humanity and Nature
2013
Kyoto University
1998-2011
We study the big-bang nucleosynthesis (BBN) with long-lived exotic particle, called $X$. If lifetime of $X$ is longer than $\ensuremath{\sim}0.1\text{ }\text{ }\mathrm{sec}$, its decay may cause nonthermal nuclear reactions during or after BBN, altering predictions standard BBN scenario. pay particular attention to hadronic modes and calculate primordial abundances light elements. Using result, we derive constraints on abundance Compared previous studies, have improved following points in...
The late-time entropy production by massive particle decay induces various cosmological effects in the early epoch and modifies standard scenario. We investigate thermalization process of neutrinos after solving Boltzmann equations numerically. find that if large is produced at $t\ensuremath{\sim}1 \mathrm{sec},$ are not thermalized very well do have perfect Fermi-Dirac distribution. Then freeze-out value neutron to proton ratio altered considerably light elements, especially...
We derive big-bang nucleosynthesis (BBN) constraints on both unstable and stable gravitino taking account of recent progress in theoretical study the BBN processes as well observations primordial light-element abundances. In case gravitino, we set upper limit reheating temperature assuming that gravitinos are mainly produced by scattering thermal particles. For consider $B$-ino, stau, sneutrino next-to-the-lightest supersymmetric particle obtain their properties. Compared with previous...
We propose a chaotic inflation model in supergravity. In the Kahler potential has Nambu-Goldstone-type shift symmetry of inflaton chiral multiplet which ensures flatness beyond Planck scale. show that naturally takes place by introducing small breaking term superpotential. This may open new branch building for inflationary cosmology framework
We review recent developments on axion cosmology. Topics include : cold dark matter, axions from topological defects, isocurvature perturbation and its non-Gaussianity axino/saxion cosmology in supersymmetric model.
The cosmological scenario where the Peccei-Quinn symmetry is broken after inflation investigated. In this scenario, topological defects such as strings and domain walls produce a large number of axions, which contribute to cold dark matter universe. previous estimations abundance are updated refined based on field-theoretic simulations with improved grid sizes. possible uncertainties originated in numerical calculations also discussed. It found that axions can be responsible for mass range...
The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO look for axions or axion-like particles (ALPs) originating in the Sun via Primakoff conversion of solar plasma photons. In terms signal-to-noise ratio, about 4–5 orders magnitude more sensitive than CAST, currently most powerful helioscope, reaching sensitivity to axion-photon couplings down few × 10−12 GeV−1 and thus probing large fraction unexplored ALP parameter space....
Primordial black holes (PBHs) are one of the candidates to explain gravitational wave (GW) signals observed by LIGO detectors. Among several phenomena in early Universe, cosmic inflation is a major example generate PBHs from large primordial density perturbations. In this paper, we discuss possibility interpret GW events as mergers which produced inflation. The curvature perturbation should be enough produce sizable amount and thus have other probes test scenario. We point out that current...
Following a new microlensing constraint on primordial black holes (PBHs) with $\ensuremath{\sim}1{0}^{20}--1{0}^{28}\text{ }\text{ }\mathrm{g}$ [H. Niikura et al., arXiv:1701.02151.], we revisit the idea of PBH as all dark matter (DM). We have shown that updated observational constraints suggest viable mass function for PBHs DM to peak at $\ensuremath{\simeq}1{0}^{20}\text{ small width $\ensuremath{\sigma}\ensuremath{\lesssim}0.1$, by imposing an extended in proper way. also provided...
We analyze the spectrum of axions radiated from collapse domain walls, which have received less attention in literature. The evolution topological defects related to axion models is investigated by performing field-theoretic lattice simulations. simulate whole process defects, including formation global strings, and annihilation due tension walls. has a peak at low frequency, implies that produced walls are not highly relativistic. revisit relic abundance cold dark matter find contribution...
We study effects of long-lived massive particles, which decay during the big-bang nucleosynthesis (BBN) epoch, on primordial abundances light elements. Compared to previous studies, (i) reaction rates standard BBN reactions are updated, (ii) most recent observational data element and cosmological parameters used, (iii) interconversion energetic nucleons at time inelastic scatterings with background nuclei considered, (iv) hadronic shower induced by high energy anti-nucleons included. compare...
Abstract The existence of a stochastic gravitational wave background is indicated by the recent pulsar timing array (PTA) experiments. We study enhanced production second-order waves from scalar perturbations when universe experiences transition early matter-dominated era to radiation-dominated due Q-ball decay. extend analysis in previous work including frequency range where density go non-linear and find that resultant spectrum can be consistent with favored PTA experiment results.
We investigate cosmological effects concerning the late-time entropy production due to decay of nonrelativistic massive particles. The thermalization process neutrinos after is properly solved by using Boltzmann equation. If a large takes place at late time $t\ensuremath{\simeq}1\mathrm{sec}$, it found that fraction cannot be thermalized. This fact loosens tight constraint on reheating temperature ${T}_{R}$ from big bang nucleosynthesis and could as low 0.5 MeV. influence scale structure...
We present the full nonlinear calculation of formation a Q ball through Affleck-Dine (AD) mechanism by numerical simulations. It is shown that large balls are actually produced fragmentation condensate scalar field whose potential very flat. find typical size determined most developed mode linearized fluctuations, and almost all initial charges which AD carries absorbed into formed balls, sizes depend only on charge densities.
It has been recently pointed out that the initial value problem in new inflation models is naturally solved by supergravity effects if there exists a pre-inflation before inflation. We study this double model details and find density fluctuations on small cosmological scales are much larger than those large due to peculiar property of show results production primordial black holes which have $\sim 1 M_{\odot}$ masses certain parameter region model. stress these may be identified with MACHOs...
We study how the oscillations of neutrinos affect their thermalization process during reheating period with temperature $O(1)$ MeV in early universe. follow evolution neutrino density matrices and investigate predictions big bang nucleosynthesis vary temperature. For several MeV, we find that including makes different predictions, especially for $^{4}\mathrm{He}$ abundance. Also, effects on lower bound from cosmological observations are discussed.
We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by use field theoretic lattice simulations with grid size 10243, which is larger than previous study. have recognized that there exists an error in code used study, and correction leads to suppression at high frequencies. The peak located scale corresponding Hubble radius time decay walls, its amplitude consistent naive estimation based on quadrupole formula. Using numerical results,...
We investigate the consistency of a scenario in which baryon asymmetry, dark matters, as well cosmic density perturbation are generated simultaneously through evaporation primordial black holes (PBHs). This can explain coincidence matter and universe, is free from isocurvature problem. show that this predicts masses PBHs, right-handed neutrinos Hubble scale during inflation, non-gaussianity running spectral index. also discuss testability by detecting high frequency gravitational waves PBHs.
We argue that the existence of cold dark matter is explained by primordial black holes.We show a significant number holes can be formed in an axion-like curvaton model, which highly blue-tilted power spectrum curvature perturbations achieved.It found produced with masses $\sim 10^{20} -10^{38} \mathrm{g}$ account for present matter.We also possibility forming mass 10^5 M_{\odot}$ as seeds supermassive holes.
We propose a novel scenario to produce abundant primordial black holes (PBHs) in new inflation which is second phase of double the supergravity framework. In our model, some preinflation before assumed and it would be responsible for curvature perturbations on cosmic microwave background scale, while produces only small scale perturbations. Our model has linear, quadratic, cubic terms its potential PBH production corresponds with flat inflection point. The linear term can interpreted come...
Primordial Black Hole (PBH) is one of the leading non-particle candidates for dark matter (DM). Although several observations severely constrain amount PBHs, it recently pointed out that there an uncertainty on microlensing constraints below $\sim 10^{-10} M_\odot$ which was ignored originally but may weaken significantly. In this paper, facing uncertainty, we investigate possibility PBHs can make up all DM in a broad mass spectrum. Moreover, propose concrete inflation model simultaneously...
We argue that a primordial black hole is natural and unique candidate for all dark matter. show that, in smooth-hybrid new double inflation model, right amount of the holes, with sharply-defined mass, can be produced at end regime, through preheating. first consider masses < 10−7M⊙ which are allowed by previous constraints. next discuss much heavier mass 105M⊙ hinted entropy, galactic size evolution, arguments. Effects on running scalar spectral index computed.