New solar x-ray constraints on keV axionlike particles

Abstract

The decay of axionlike particles (ALPs) trapped in the solar gravitational field would contribute to the observed solar x-ray flux, hence constraining ALP models. We improve by one order of magnitude the existing limits in the parameter space (gaγγ, m) by considering ALPs production via photon coalescence. For gae≠0, we demonstrate that trapped ALPs can be Compton absorbed while crossing the Sun, resulting in two regimes in the exclusion limits, with a transition triggered by gae. Out of the transitional region, the solar x-ray constraints on ALPs are exclusively governed by gaγγ.