# Freeze-in Axion-like Dark Matter

## TL;DR

This paper introduces a Higgs portal model where an axion-like particle (ALP) acts as stable or long-lived dark matter, with its properties governed by shift symmetry and potential UV completions involving hidden sectors.

## Contribution

It proposes a novel Higgs portal ALP model for freeze-in dark matter, detailing mechanisms for coupling generation and stability preservation.

## Key findings

- ALP can serve as a stable freeze-in dark matter candidate.
- UV completions can involve hidden confining sectors or radiative corrections.
- Suppression of ALP decay is achievable through additional symmetries.

## Abstract

We present an interesting Higgs portal model where an axion-like particle (ALP) couples to the Standard Model sector only via the Higgs field. The ALP becomes stable due to CP invariance and turns out to be a natural candidate for freeze-in dark matter because its properties are controlled by the perturbative ALP shift symmetry. The portal coupling can be generated non-perturbatively by a hidden confining gauge sector, or radiatively by new leptons charged under the ALP shift symmetry. Such UV completions generally involve a CP violating phase, which makes the ALP unstable and decay through mixing with the Higgs boson, but can be sufficiently suppressed in a natural way by invoking additional symmetries.