Looking for Lights from the Darkness: Signals from MeV-scale Solar Axion-like Particles

TL;DR

This paper proposes new methods to detect MeV-scale solar axion-like particles through their unique photon signals, using space and terrestrial experiments, potentially surpassing current supernova constraints.

Contribution

It introduces novel detection strategies based on angular and spectral photon distributions from axion decay, with sensitivity estimates exceeding existing limits.

Findings

Potential to probe axion-photon coupling up to 3×10^{-12} GeV^{-1}

Space and terrestrial experiments can detect photons with sensitivities of 10^{-16} to 10^{-17} erg cm^{-2} s^{-1}

Existence of a critical height affecting terrestrial detection due to geometric effects

Abstract

The axion-like particles $a$ can be produced in the Sun via the process of $p + D \to {}^3{\rm He} +a$, with mass up to 5.5 MeV. The photons in the subsequent decay $a \to \gamma\gamma$ can deviate significantly from the Sun, or even from roughly the opposite direction of the Sun. The nontrivial angular and spectral distributions of such photons enable us new methods to detect the {\it lights from the darkness}. In this letter, we consider both the space detection and terrestrial experiments at the South Pole. As a result of the two-body decay and the geometric effects, there exists a critical height for the terrestrial experiments, below which there is no photon for some regions of the parameter space. With the sensitivities of $10^{-16}$ ($10^{-17}$) erg cm$^{-2}$ s$^{-1}$ for the MeV-scale photons in future space and terrestrial experiments, the coupling $g_{a\gamma}$ of $a$ to photons can be probed up to $3\times10^{-12}$ ($1\times10^{-12}$) GeV$^{-1}$, well surpassing the current supernova limits.