15 citations · 48 across the 10 of their papers we have counts for
12 papers
Axion Isocurvature Perturbations Survive the Scaling Evolution of Axion Domain Walls
Naoya Kitajima, Junseok Lee, Kai Murai +2
We revisit the evolution of axion domain walls seeded by inflationary fluctuations. In our previous work, we showed that such domain-wall networks retain superhorizon correlations…
Multi-field oscillons/I-balls in the Friedberg-Lee-Sirlin model
Kai Murai, Tatsuya Ogawa, Fuminobu Takahashi
We study oscillon/I-ball solutions in a real scalar version of the Friedberg-Lee-Sirlin (FLS) model. Using the multiple-scale analysis, we derive the conditions for oscillon soluti…
Sign-Flipping Axion Potentials via Kapitza-Type Modulation by Heavy Axions
Kai Murai, Fuminobu Takahashi, Kosei Tomiyama
We show that the potential of a light axion can flip sign, or even nearly vanish, as a result of coherent oscillations of a heavier axion with which it mixes. This phenomenon is an…
Dynamical Prevention of Topological Defect Formation
Junseok Lee, Kai Murai, Kazunori Nakayama +1
Topological defects can have significant cosmological consequences, so their production must be examined carefully. It is usually assumed that topological defects are produced if t…
Resolving the QCD Axion Domain Wall Problem with a Light Axion
Junseok Lee, Kai Murai, Fuminobu Takahashi +1
We propose two novel solutions to the domain wall problem of the QCD axion by introducing a massless or light axion that also couples to gluons. The first solution applies when the…
Q-balls Under Spontaneously Broken U(1) Symmetry
Masahiro Kawasaki, Kai Murai, Fuminobu Takahashi
We study the evolution of Q-balls under a spontaneously broken global symmetry. Q-balls are stabilized by the conservation of charge, but when the symmetry is spontan…
Why ? Anthropic Selection in a + Axion Dark Energy Model
Kai Murai, Fuminobu Takahashi
We study a dark energy model composed of a bare negative cosmological constant and a single ultra-light axion, motivated by the string axiverse. Assuming that intelligent observers…
Isotropic cosmic birefringence from string axion domain walls without cosmic strings, and DESI results
Junseok Lee, Kai Murai, Fuminobu Takahashi +1
Recently, results from the Atacama Cosmology Telescope (ACT) DR6 have shown a preference for isotropic cosmic birefringence, consistent with previous analyses based on Planck and W…
Primordial Black Hole Formation via Inverted Bubble Collapse
Kai Murai, Kodai Sakurai, Fuminobu Takahashi
We propose a novel mechanism of primordial black hole (PBH) formation through inverted bubble collapse. In this scenario, bubbles nucleate sparsely in an incomplete first-order pha…
QCD Axion Dark Matter from level crossing with refined adiabatic condition
Kai Murai, Yuma Narita, Fuminobu Takahashi +1
We investigate the level-crossing phenomenon in two-axion systems, where the mass eigenvalues intersect as the mass of one axion increases with the cooling of the universe. This ph…
More is Different: Multi-Axion Dynamics Changes Topological Defect Evolution
Junseok Lee, Kai Murai, Fuminobu Takahashi +1
We study topological defects in multi-axion models arising from multiple Peccei-Quinn (PQ) scalars. Using a simplified two-axion system, we reveal fundamental differences in the ev…
Induced Domain Walls of QCD Axion, and Gravitational Waves
Junseok Lee, Kai Murai, Fuminobu Takahashi +1
We show that heavy axion domain walls induce domain walls of the QCD axion through a mixing between the heavy axion and the QCD axion, even when the pre-inflationary initial condit…