Kazunori Kohri
A5016484890- Cosmology and Gravitation Theories
- Dark Matter and Cosmic Phenomena
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Particle physics theoretical and experimental studies
- Black Holes and Theoretical Physics
- Geophysics and Gravity Measurements
- Radio Astronomy Observations and Technology
- Kidney Stones and Urolithiasis Treatments
- Neutrino Physics Research
- Galaxies: Formation, Evolution, Phenomena
- Particle Detector Development and Performance
- Solar and Space Plasma Dynamics
- Astrophysical Phenomena and Observations
- Relativity and Gravitational Theory
- Bone and Dental Protein Studies
- Urological Disorders and Treatments
- Pediatric Urology and Nephrology Studies
- Radiation Therapy and Dosimetry
- Bladder and Urothelial Cancer Treatments
- Superconducting and THz Device Technology
- Astronomy and Astrophysical Research
- Parathyroid Disorders and Treatments
- Radiation Detection and Scintillator Technologies
High Energy Accelerator Research Organization
2016-2025
Kavli Institute for the Physics and Mathematics of the Universe
2019-2025
The University of Tokyo
2006-2025
The Graduate University for Advanced Studies, SOKENDAI
2016-2025
National Astronomical Observatory of Japan
2022-2025
Institute of Particle and Nuclear Studies
2014-2024
International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles
2022-2024
Universitat de Barcelona
2024
Institut d'Estudis Espacials de Catalunya
2024
Japan Aerospace Exploration Agency
2024
We update the constraints on fraction of Universe going into primordial black holes in mass range 10^9--10^17 g associated with effects their evaporations big bang nucleosynthesis and extragalactic photon background. include for first time all quark gluon emission by these account latest observational developments. then discuss other this show that are weaker than background limits, apart from a small 10^13--10^14 g, where damping cosmic microwave anisotropies dominates. Finally we review...
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 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...
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...
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...
Whether or not the primordial gravitational wave (GW) produced during inflation is sufficiently strong to be observable, GWs are necessarily from curvature perturbations in second order of perturbation. The induced can enhanced by at small scales presence matter-dominated stages cosmological history. We analytically calculate integral expression power spectrum which a universal part independent perturbations. This makes subsequent numerical integrals significantly easy. In simple cases, we...
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...
Based on a physical argument, we derive new analytic formula for the amplitude of density perturbation at threshold primordial black hole formation in universe dominated by perfect fluid with equation state $p=w\rho c^{2}$ $w\ge 0$. The gives $\delta^{\rm UH}_{H c}=\sin^{2}[\pi \sqrt{w}/(1+3w)]$ and $\tilde{\delta}_{c}=[3(1+w)/(5+3w)]\sin^{2}[\pi\sqrt{w}/(1+3w)]$, where c}$ $\tilde{\delta}_{c}$ are horizon crossing time uniform Hubble slice measure used numerical simulations, respectively,...
Abstract The Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is a future Japanese space mission with frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection primordial gravitational waves, which could have been 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...
Stellar-mass Primordial Black Holes (PBH) have been recently reconsidered as a Dark Matter (DM) candidate, after the aLIGO discovery of several binary BH mergers with masses tens $M_\odot$. accretion on such massive objects leads to emission high-energy photons, capable altering ionization and thermal history universe. This in turn affects statistical properties cosmic microwave background (CMB) anisotropies. Previous analyses assumed spherical accretion. We argue that this approximation...
Even if massive ($10\,M_\odot \lesssim M 10^4 M_\odot$) primordial black holes (PBHs) can only account for a small fraction of the dark matter (DM) in universe, they may still be responsible sizable coalescence events measured by LIGO/Virgo, and/or act as progenitors supermassive (SMBHs) observed already at high redshift ($z\gtrsim 6$). In presence dominant, non-PBH DM component, bounds set CMB via an altered ionization history are modified. We revisit cosmological accretion halo around PBHs...
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...
DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) 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. will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by differential Fabry-Perot interferometer, four units triangular...
Abstract LiteBIRD, the Lite (Light) satellite for study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission primordial cosmology fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as strategic large-class (L-class) mission, with an expected launch late 2020s using JAXA’s H3 rocket. planned to orbit Sun–Earth Lagrangian point L2, where it will map microwave over entire sky three years, telescopes 15...
Extended results on the cosmic-ray electron $+$ positron spectrum from 11 GeV to 4.8 TeV are presented based observations with Calorimetric Electron Telescope (CALET) International Space Station utilizing data up November 2017. The analysis uses full detector acceptance at high energies, approximately doubling statistics compared previous result. CALET is an all-calorimetric instrument a total thickness of 30 ${X}_{0}$ normal incidence and fine imaging capability, designed achieve large...
The NANOGrav collaboration for the pulsar timing array (PTA) observation recently announced evidence of an isotropic stochastic process, which may be first detection gravitational-wave (GW) background. We discuss possibility that signal is caused by second-order GWs associated with formation solar-mass primordial black holes (PBHs). This can tested future interferometer-type GW observations targeting from merger events PBHs as well updates PTA observations.
For a variety of ongoing and planned gravitational-wave (GW) experiments, we study expected constraints on the fraction (${f}_{\mathrm{PBH}}$) primordial black holes (PBHs) in dark matter by evaluating energy-density spectra two kinds stochastic GW backgrounds. The first one is produced from an incoherent superposition GWs emitted coalescences all binary PBHs. second induced through nonlinear mode couplings large curvature perturbations inevitably associated with generation PBHs early...
In this paper, we present the analysis and results of a direct measurement cosmic-ray proton spectrum with CALET instrument onboard International Space Station, including detailed assessment systematic uncertainties. The observation period used in is from October 13, 2015 to August 31, 2018 (1054 days). We have achieved very wide energy range necessary carry out measurements 50 GeV 10 TeV covering, for first time space, single whole interval previously investigated most cases separate...
Voyage 2050 White Paper highlighting the unique science opportunities using spectral distortions of cosmic microwave background (CMB). CMB probe many processes throughout history Universe. Precision spectroscopy, possible with existing technology, would provide key tests for expected within cosmological standard model and open an enormous discovery space to new physics. This offers scientific furthering our understanding inflation, recombination, reionization structure formation as well dark...
Multiple pulsar timing array (PTA) collaborations recently announced the evidence of common-spectral processes caused by gravitational waves (GWs). These can be stochastic GW background and its origin may astrophysical and/or cosmological. We interpret it as GWs induced primordial curvature perturbations discuss their implications on black holes (PBHs). show that newly released data suggest PBHs much lighter than Sun [$\mathcal{O}({10}^{\ensuremath{-}4}){M}_{\ensuremath{\bigodot}}$ for...
The energy injection through Hawking evaporation has been used to put strong constraints on primordial black holes as a dark matter candidate at masses below $10^{17}\,\rm{g}$. However, Hawking's semiclassical approximation breaks down latest after half-decay. Beyond this point, the could be significantly suppressed, was shown in recent work. In study, we review existing cosmological and astrophysical bounds holes, taking effect into account. We show that disappear completely for reasonable...