Axion cosmology in the presence of non-trivial Nambu-Goldstone modes

Abstract

Axion cosmology is reexamined taking into account effect of kinetic pseudo Nambu-Goldstone modes, with its importance recently pointed out. When Peccei-Quinn (PQ) symmetry is broken by a chiral U(1) singlet, it is found that the effect of kinetic Nambu-Goldstone mode makes the axion dark matter untenable. When PQ symmetry is extended and is broken by two singlets, we find axion cosmology to work, but there are several differences from the axion cosmology studied in the literature. The differences are (1) ordinary type of dark matter scaling as $1/{\rm cosmic \; scale\; factor}^3$ arising from a modulus field and not from the usual angular field, (2) mass of the dark matter quantum in the ultralight range, $(10^{-32} \sim 10^{-14})\,$eV, (3) emergence of dark energy with the present density of order (a few meV)$^4$ consistent with observations, (4) presence of a long range spin-dependent force, (5) slow-roll inflation after PQ symmetry breaking when conformal coupling to gravity is introduced.