104 citations · 676 across the 37 of their papers we have counts for
37 papers
Lattice study of primordial black hole formation in bumpy axion inflation
Masahiro Kawasaki, Kai Murai, Shunsuke Tsuchida
We study primordial black hole (PBH) formation in axion inflation using lattice simulations. In axion inflation with a bumpy potential, the curvature perturbations ca…
Merger rate of initially clustered primordial black holes for the two-body channel
Kentaro Kasai, Masahiro Kawasaki, Kai Murai +1
Primordial black holes (PBHs) may form an initially clustered population depending on their production mechanism. Motivated by binary black-hole merger events observed by gravitati…
Microlensing events and primordial black holes in the axionlike curvaton model
Kentaro Kasai, Masahiro Kawasaki, Kai Murai +1
Recently, Subaru Hyper Suprime-Cam (HSC) observations found 12 candidates for microlensing events. These events can be explained by primordial black holes (PBHs) with masses of $10…
Resonant production of sterile neutrino dark matter with a refined numerical scheme
Kentaro Kasai, Masahiro Kawasaki, Kai Murai
The existence of a large primordial neutrino asymmetry is an intriguing possibility, both observationally and theoretically. Such an asymmetry can lead to the resonant production o…
EMPRESS. XV. A New Determination of the Primordial Helium Abundance Suggesting a Moderately Low Value
Hiroto Yanagisawa, Masami Ouchi, Akinori Matsumoto +18
We present a new constraint on the primordial helium abundance, , based on Subaru observations. A major source of uncertainty in previous determination…
EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall
Kimihiko Nakajima, Masami Ouchi, Yuki Isobe +47
Using the Subaru/FOCAS IFU capability, we examine the spatially resolved relationships between gas-phase metallicity, stellar mass, and star-formation rate surface densities (Sigma…
Supermassive black hole formation from Affleck-Dine mechanism with suppressed clustering on large scales
Kentaro Kasai, Masahiro Kawasaki, Kai Murai +1
We study a primordial black hole (PBH) formation model based on the framework of the inhomogeneous Affleck-Dine (AD) mechanism, which can explain the seeds of supermassive black ho…
Affleck-Dine leptogenesis scenario for resonant production of sterile neutrino dark matter
Kentaro Kasai, Masahiro Kawasaki, Kai Murai
Sterile neutrino is a fascinating candidate for dark matter. In this paper, we examine the Affleck-Dine (AD) leptogenesis scenario generating a large lepton asymmetry, which can in…
Misalignment production of vector boson dark matter from axion-SU(2) inflation
Tomohiro Fujita, Kai Murai, Kazunori Nakayama +1
We present a new mechanism to generate a coherently oscillating dark vector field from axion-SU(2) gauge field dynamics during inflation. The SU(2) gauge field acquires a nonzero b…
Primordial Origin of Supermassive Black Holes from Axion Bubbles
Kentaro Kasai, Masahiro Kawasaki, Naoya Kitajima +3
We study a modification of the primordial black hole (PBH) formation model from axion bubbles. We assume that the Peccei-Quinn scalar rolls down in the radial direction from a larg…
Enhancement of gravitational waves at Q-ball decay including non-linear density perturbations
Masahiro Kawasaki, Kai Murai
The existence of a stochastic gravitational wave background is indicated by the recent pulsar timing array (PTA) experiments. We study the enhanced production of second-order gravi…
Can baryon asymmetry be explained by a large initial value before inflation?
Kai Murai, Fuminobu Takahashi, Masaki Yamada +1
We show that the baryon asymmetry of the Universe cannot be explained by a large initial value before inflation because it inevitably predicts correlated baryon isocurvature pertur…
A Novel Probe of Supersymmetry in Light of Nanohertz Gravitational Waves
Kai Murai, Wen Yin
A new era of exploring the early Universe may have begun with the recent strong evidence for the stochastic gravitational wave (GW) background from the data reported by NANOGrav, E…
Gravitational Waves from Domain Wall Collapse, and Application to Nanohertz Signals with QCD-coupled Axions
Naoya Kitajima, Junseok Lee, Kai Murai +2
We study for the first time the gravitational waves generated during the collapse of domain walls, incorporating the potential bias in the lattice simulations. The final stages of…
The QCD Axion: A Unique Player in the Axiverse with Mixings
Kai Murai, Fuminobu Takahashi, Wen Yin
In an axiverse with numerous axions, the cosmological moduli problem poses a significant challenge because the abundance of axions can easily exceed that of dark matter. The well-e…
Clustering of Primordial Black Holes from QCD Axion Bubbles
Kentaro Kasai, Masahiro Kawasaki, Naoya Kitajima +3
We study the clustering of primordial black holes (PBHs) and axion miniclusters produced in the model proposed to explain the LIGO/Virgo events or the seeds of the supermassive bla…
Constraint on Early Dark Energy from Isotropic Cosmic Birefringence
Johannes R. Eskilt, Laura Herold, Eiichiro Komatsu +3
Polarization of the cosmic microwave background (CMB) is sensitive to new physics violating parity symmetry, such as the presence of a pseudoscalar "axionlike" field. Such a field…
EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies
Yi Xu, Masami Ouchi, Yuki Isobe +49
We present demography of the dynamics and gas-mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of and low stellar masses of $10^4-…
Muon and non-thermal leptogenesis in model
Shintaro Eijima, Masahiro Ibe, Kai Murai
The gauged symmetry is the simplest possibility to explain the observed muon , while being consistent with the neutrino oscillations through the seesaw mechan…
Enhancement of second-order gravitational waves at Q-ball decay
Shinta Kasuya, Masahiro Kawasaki, Kai Murai
The recent observation of He favors a large lepton asymmetry at the big bang nucleosynthesis. If Q-balls with a lepton charge decay after the electroweak phase transition, such…
Isotropic cosmic birefringence from early dark energy
Kai Murai, Fumihiro Naokawa, Toshiya Namikawa +1
A tantalizing hint of isotropic cosmic birefringence has been found in the cross-power spectrum of the cosmic microwave background (CMB) polarization data with a statistical…
Revisiting the Affleck-Dine mechanism for primordial black hole formation
Kentaro Kasai, Masahiro Kawasaki, Kai Murai
We study a primordial black hole (PBH) formation scenario based on the Affleck-Dine (AD) mechanism and investigate two PBH mass regions: motivated by the LIGO-V…
Gravitational waves detectable in laser interferometers from axion-SU(2) inflation
Tomohiro Fujita, Kaname Imagawa, Kai Murai
Chromo-natural inflation (CNI) is an inflationary model where an axion coupled with SU gauge fields acts as the inflaton. In CNI, the gauge fields have nonzero vacuum expectat…
Lepton Asymmetric Universe
Masahiro Kawasaki, Kai Murai
The recent observation of He implies that our universe has a large lepton asymmetry. We consider the Affleck-Dine (AD) mechanism for lepton number generation. In the AD mechani…