Wormhole-Induced ALP Dark Matter

TL;DR

This paper explores how non-perturbative gravitational effects can give axion-like particles (ALPs) a wide range of masses, allowing them to be viable dark matter candidates through various production mechanisms in different inflationary scenarios.

Contribution

It demonstrates that gravitationally induced symmetry breaking can produce ALPs with a broad mass spectrum capable of accounting for dark matter, considering multiple inflationary models and formalisms.

Findings

ALPs can have masses from 10^{-21} eV to TeV as dark matter.

Allowed parameter ranges depend on inflationary scenario and symmetry breaking scale.

ALPs could be the dominant dark matter component in various models.

Abstract

Non-perturbative gravitational effects induce explicit global symmetry breaking terms within axion models. These exponentially suppressed terms in the potential give a mass contribution to the axion-like particles (ALPs). In this work we investigate this scenario with a scalar field charged under a global $U(1)$ symmetry and having a non-minimal coupling to gravity. Given the exponential dependence, the ALP can retain a mass spanning a wide range, which can act as a dark matter component. We specify pre-inflationary and post-inflationary production mechanisms of these ALPs, with the former from the misalignment mechanism and the latter from both the misalignment and cosmic-string decay. We identify the allowed parameter ranges that explain the dark matter abundance for both a general inflation case and a case where the radial mode scalar drives inflation, each in metric and Palatini formalisms. We show that the ALP can be the dominant component of the dark matter in a wide range of its mass, $m_{a} \in [10^{-21}~\mathrm{eV},\, \mathrm{TeV}]$, depending on the inflationary scenario and the $U(1)$ breaking scale. These results indicate that ALPs can be responsible for our dark matter abundance within a setup purely from non-perturbative gravitational effects.