Phenomenology of CP-even ALP

TL;DR

This paper explores the properties, collider signatures, and cosmological implications of a CP-even axion-like particle (ALP), proposing it as a viable dark matter candidate with distinctive experimental signals.

Contribution

It introduces the concept of a CP-even ALP in simple renormalizable models and studies its collider phenomenology and cosmological roles, including dark matter potential.

Findings

CP-even ALP can be produced from Higgs decay in colliders.

Distinctive signals include Higgs exotic decays and displaced vertices.

CP-even ALP as a dark matter candidate detectable via astrophysical observations.

Abstract

Axion or axion-like particle (ALP) has been usually considered as a CP-odd Nambu-Goldstone boson (NGB) from the spontaneous breakdown of a global U(1) symmetry. In this paper, we point out that the NGB behaves as a CP-even particle coupled to the SM particles in a large class of simple (or perhaps the simplest) renormalizable models. We provide a first study of the collider phenomenology and cosmology of the CP-even ALP. In a natural parameter region, the CP-even ALP can be produced from the Higgs boson decay in colliders. When the mass is not very light, the signals will be Higgs exotic decays, Higgs decay to displaced vertex $\times 2$, Higgs decay to displaced vertex + missing energy. The signal can be discriminated from other models, e.g. hidden photon, by measuring the decay length and the decay products of the light new particle. In addition, when $ m_a\lesssim \,$MeV, in which case the Higgs boson invisible decay may be probed in the colliders, the CP-even ALP is a nice Dark matter (DM) candidate. The DM can be probed by 21cm line measurement, the future measurement of the Milky way mass halo function in the Vera Rubin Observatory, as well as X- or $\gamma$-ray observations. The DM production mechanisms are discussed.