Axion-Like Electrophilic Portal for Pion Dark Matter

TL;DR

This paper explores a model where axion-like particles serve as a portal between dark matter and the Standard Model, with potential relevance to the X17 anomaly and dark sector physics.

Contribution

It introduces a minimal SIMP dark matter model coupled to an ALP that interacts with electrons, expanding the viable parameter space and linking to experimental anomalies.

Findings

ALP with mass around 10 MeV can connect dark matter and visible sectors.

The parameter space is broader than previous models, accommodating heavier ALPs.

The model's parameter space overlaps with the X17 anomaly region.

Abstract

We investigate a scenario where Strongly Interacting Massive Particle (SIMP) dark matter interacts with an axion-like particle (ALP) that couples exclusively to electrons. This minimal setup provides interactions which enforce thermal equilibrium between dark matter and the SM in the early Universe. We analyze the cosmological evolution of the dark sector and the constraints arising from dark matter annihilations, ALP laboratory searches and astrophysical observations. Our results show that the allowed parameter space is wider than previous studies and an ALP with mass $m_a \sim {\cal O}(10)~\text{MeV}$ can act as a viable portal between the visible and dark sectors. Interestingly, this mass range overlaps with the parameter space suggested by the reported $X_{17}$ anomaly. Furthermore, the introduction of non-vanishing $\theta$ angle in the dark sector of the model opens up the parameter space to heavy ALP masses.