254 citations · 1.8k across the 51 of their papers we have counts for
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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…
A Bound on Light Dark Photon Dark Matter
Naoya Kitajima, Shota Nakagawa, Fuminobu Takahashi +1
We derive a bound on dark photon dark matter scenarios where the dark photon mass is generated through the Higgs mechanism, based on the requirement that symmetry breaking must occ…
Stability of domain walls with inflationary fluctuations under potential bias, and gravitational wave signatures
Naoya Kitajima, Junseok Lee, Fuminobu Takahashi +1
A recent study has shown that domain walls with inflationary initial fluctuations exhibit remarkable stability against population bias due to long-range correlations, challenging t…
Nanohertz gravitational waves from cosmic strings and dark photon dark matter
Naoya Kitajima, Kazunori Nakayama
The recent observations by pulsar timing array (PTA) experiments suggest the existence of stochastic gravitational wave background in the nano-Hz range. It can be a hint for the ne…
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…
Resonant production of dark photons from axion without a large coupling
Naoya Kitajima, Fuminobu Takahashi
Dark photons could be produced resonantly by the oscillating axion field in the early universe. This resonant production mechanism has been used in various contexts, including dark…