104 citations · 676 across the 37 of their papers we have counts for
21 papers · 1 filter
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…
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…
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…
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…
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…
EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension
Akinori Matsumoto, Masami Ouchi, Kimihiko Nakajima +42
The primordial He abundance is a powerful probe of cosmology. Currently, is best determined by observations of metal-poor galaxies, while there are on…
Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of Ultra-light Axion-like Particle
Masahiro Kawasaki, Kazuyoshi Miyazaki, Kai Murai +2
Ultra-light axion-like particle (ULAP) with mass has recently been attracting attention as a possible solution to the small-scale crisis. ULAP forms…
Gravitational wave trispectrum in the axion-SU(2) model
Tomohiro Fujita, Kai Murai, Ippei Obata +1
We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation. In non-Abelian gauge…
Strong clustering of primordial black holes from Affleck-Dine mechanism
Masahiro Kawasaki, Kai Murai, Hiromasa Nakatsuka
Primordial black hole (PBH) is a fascinating candidate for the origin of binary merger events observed by LIGO-Virgo collaboration. The spatial distribution of PBHs at formation is…
Detection of isotropic cosmic birefringence and its implications for axion-like particles including dark energy
Tomohiro Fujita, Kai Murai, Hiromasa Nakatsuka +1
We investigate the possibility that axion-like particles (ALPs) with various potentials account for the isotropic birefringence recently reported by analyzing the Planck 2018 polar…
Statistically-Anisotropic Tensor Bispectrum from Inflation
Takashi Hiramatsu, Kai Murai, Ippei Obata +1
We develop a possibility of generating tensor non-Gaussianity in a kind of anisotropic inflation, where a gauge field is kinetically coupled to a spectator scalar field. Owi…
Probing Axion-like Particles via CMB Polarization
Tomohiro Fujita, Yuto Minami, Kai Murai +1
Axion-like particles (ALPs) rotate the linear polarization of photons through the ALP-photon coupling and convert the cosmic microwave background (CMB) -mode to the -mode. We…
Formation of supermassive primordial black holes by Affleck-Dine mechanism
Masahiro Kawasaki, Kai Murai
We study the supermassive black holes (SMBHs) observed in the galactic centers. Although the origin of SMBHs has not been well understood yet, previous studies suggest that seed bl…