583 citations · 2.8k across the 35 of their papers we have counts for
36 papers
Formation of Supermassive Black Hole Seeds from Vacuum-Dependent Thermal Dark Matter
Masahiro Kawasaki, Jie Sheng, Tsutomu T. Yanagida
The origin of supermassive black holes, especially those already present at high redshift, remains an open problem. We propose that their seeds are primordial black holes formed fr…
High-Quality Axion Dark Matter without Isocurvature Problem
Masahiro Kawasaki, Jie Sheng, Tsutomu T. Yanagida
Axion dark matter in high-scale inflation is subject to the isocurvature constraint, since quantum fluctuations of the axion field during inflation may exceed the current CMB bound…
Axion Curvaton Model for the Gravitational Waves Observed by Pulsar Timing Arrays
Keisuke Inomata, Masahiro Kawasaki, Kyohei Mukaida +1
The stochastic gravitational wave background (SGWB) recently detected by the PTA collaborations could be the gravitational waves (GWs) induced by curvature perturbations. However,…
511 keV Gamma Ray from Moduli Decay in the Galactic Bulge
M. Kawasaki, T. Yanagida
We show that the decay of a light scalar boson of mass 1-10 MeV may account for the fluxes of 511 keV gamma ray observed by SPI/INTEGRAL. We argue that candidates of such…
Realistic cosmological model with dynamical cancellation of vacuum energy
A. D. Dolgov, M. Kawasaki
We propose a model with a compensating scalar field whose back reaction to the cosmological curvature cancels possible vacuum energy density down to the terms of the order of the t…
Constraints on the Star Formation Rate from Supernova Relic Neutrino Observations
M. Fukugita, M. Kawasaki
We discuss the implication of the observation of supernova relic neutrinos on the study of the star formation rate (SFR) in galaxies. The limit recently obtained at Super-Kamiokand…
Constraining the variation of the coupling constants with big bang nucleosynthesis
Kazuhide Ichikawa, M. Kawasaki
We consider the possibility of the coupling constants of the gauge interactions at the time of big bang nucleosynthesis having taken different values…
Radiative decay of a massive particle and the non-thermal process in primordial nucleosynthesis
M. Kawasaki, K. Kohri, Takeo Moroi
We consider the effects on big bang nucleosynthesis (BBN) of the radiative decay of a long-lived massive particle. If high-energy photons are emitted after the BBN epoch ($t \sim 1…
Natural Chaotic Inflation in Supergravity and Leptogenesis
M. Kawasaki, Masahide Yamaguchi, T. Yanagida
We comprehensively investigate a chaotic inflation model proposed recently in the framework of supergravity. In this model, the form of Kähler potential is determined by a symmetry…
MeV-scale Reheating Temperature and Thermalization of Neutrino Background
M. Kawasaki, K. Kohri, Naoshi Sugiyama
The late-time entropy production by the massive particle decay induces the various cosmological effects in the early epoch and modify the standard scenario. We investigate the ther…
Double inflation in supergravity and the primordial black hole formation
Toshiyuki Kanazawa, M. Kawasaki, T. Yanagida
We study a double inflation model (a hybrid inflation + a new inflation) in supergravity and discuss the formation of primordial black holes (PBHs) with mass \sim 10^{-20}-10^{5}M_…
Double Inflation in Supergravity and the Large Scale Structure
Toshiyuki Kanazawa, M. Kawasaki, Naoshi Sugiyama +1
The cosmological implication of a double inflation model with hybrid + new inflations in supergravity is studied. The hybrid inflation drives an inflaton for new inflation close to…
Initial condition for new inflation in supergravity
T. Asaka, M. Kawasaki, Masahide Yamaguchi
We study the initial value problem of new inflation models in the scheme of supergravity. We find that an inflaton generally acquires a mass of the order of the Hubble parameter vi…
Cosmological Moduli Problem and Thermal Inflation Models
T. Asaka, M. Kawasaki
In superstring theories, there exist various dilaton and modulus fields which masses are expected to be of the order of the gravitino mass . These fields lead to serious c…
Superheavy Dark Matter and Thermal Inflation
T. Asaka, M. Kawasaki, T. Yanagida
The thermal inflation is the most plausible mechanism that solves the cosmological moduli problem naturally. We discuss relic abundance of superheavy particle in the presence o…
Cosmological Constraints on Late-time Entropy Production
M. Kawasaki, K. Kohri, Naoshi Sugiyama
We investigate cosmological effects concerning the late-time entropy production due to the decay of non-relativistic massive particles. The thermalization process of neutrinos afte…
R-Invariant Topological Inflation
K. -I. Izawa, M. Kawasaki, T. Yanagida
We propose a topological inflation model in the framework of supergravity with invariance. This topological inflation model is not only free from the initial value problem of t…
Primordial Black Hole Formation in Supergravity
M. Kawasaki, T. Yanagida
We study a double inflation model (a preinflation + a new inflation) in supergravity and discuss the formation of primordial black holes which may be identified with massive compac…
Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis
Erich Holtmann, M. Kawasaki, K. Kohri +1
The effects of radiatively decaying, long-lived particles on big-bang nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after BBN, they may change the abundan…
Observational Implications of Axionic Isocurvature Fluctuations
Toshiyuki Kanazawa, M. Kawasaki, Naoshi Sugiyama +1
The axion is the most attractive candidate to solve the strong CP problem in QCD. If it exists, the inflationary universe produces axion fluctuations which are mixtures of isocurva…
Isocurvature Fluctuations of the M-theory Axion in a Hybrid Inflation Model
Toshiyuki Kanazawa, M. Kawasaki, Naoshi Sugiyama +1
The M-theory, the strong-coupling heterotic string theory, presents various interesting new phenomenologies. The M-theory bulk axion is one of these. The decay constant in this con…
Spectrum of Background X-rays from Moduli Dark Matter
T. Asaka, J. Hashiba, M. Kawasaki +1
We examine the -ray spectrum from the decay of the dark-matter moduli with mass keV, in particular, paying attention to the line spectrum from the moduli tra…
Cosmological Moduli Problem in Gauge-mediated Supersymmetry Breaking Theories
T. Asaka, J. Hashiba, M. Kawasaki +1
A generic class of string theories predicts the existence of light moduli fields, and they are expected to have masses comparable to the gravitino mass which is in…
Primordial Black Hole Formation in a Double Inflation Model in Supergravity
M. Kawasaki, N. Sugiyama, T. Yanagida
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 the new i…