Impacts of Axion-Like Particle on the Constraints of Dark Photon

A dark sector may exist and interact with the Standard Model (SM) through the U(1) kinetic mixing. Through this portal-type interaction, the dark photon from the dark sector couples to SM fermions, and may explain the discrepancy between experimental data and SM calculations on the muon anomalous magnetic moment, muon g-2. However, current searches for the dark photon impose stringent constraints on the mixing parameter ε for various dark photon masses, excluding the favorite parameter space for muon g-2. In this paper, we study the case where a global U(1) in the dark sector is spontaneously broken, resulting in a light pseudo-Goldstone, axion-like particle (ALP) a, which couples to the dark photon and SM photon. Through the dark photon–ALP–photon interaction, the dark photon may decay into a photon and an ALP when this channel is kinematically allowed. As a result, the experimental constraints on the dark photon change significantly, and the dark photon is able to explain the muon g-2 anomaly when its mass is heavier than 10 GeV.