I present an introduction and topical review on axions as a dark matter candidate. Emphasis
is placed on issues surrounding the cosmology of axion dark matter that are relevant for …

A bstract String theory has been claimed to give rise to natural fuzzy dark matter candidates
in the form of ultralight axions. In this paper we revisit this claim by a detailed study of how …

Taking the recently reported nonzero rotation angle of the cosmic microwave background
(CMB) linear polarization β= 0.35±0.14 deg as the hint for a pseudo–Nambu-Goldstone …

Recently, a low-z measurement of the Hubble constant, H 0= 73.04±1.04 km/s/Mpc, was
reported by the SH0ES Team. The long-standing Hubble tension, ie the difference between …

The recently reported non-zero isotropic birefringence angle in Planck 2018 polarization
data provides a tantalizing hint for new physics of axions. In this paper, we explain this by a …

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 …

We examine the theoretical possibility for the heavy QCD axion to induce slow-roll inflation
while solving the strong CP problem through the Peccei-Quinn mechanism. If the …

When the inflaton is coupled to the gluon Chern-Simons term for successful reheating,
mixing between the inflaton and the QCD axion is generally expected given the solution of …

We study cosmological effects of explicit Peccei-Quinn breaking on the QCD axion dark
matter. We find that the axion abundance decreases or increases significantly depending on …

We show that a recent constraint on the cosmic birefringence effect due to dark energy can
be related to the constraints on the coupling of axion dark matter to photon, by relying on a …