21 cm forest probes on axion dark matter in postinflationaryPeccei-Quinn symmetry breaking scenarios

Abstract

© 2020 American Physical Society. We study the future prospects of the 21 cm forest observations on the axionlike dark matter when the spontaneous breaking of global Peccei-Quinn (PQ) symmetry occurs after the inflation. The large isocurvature perturbations of order unity sourced from axionlike particles can result in the enhancement of minihalo formation, and the subsequent hierarchical structure formation can affect the minihalo abundance whose masses can exceed O(104) M relevant for the 21 cm forest observations. We show that the 21 cm forest observations are capable of probing the axionlike particle mass in the range 10-18 ma 10-12 eV for the temperature independent axion mass. For the temperature dependent axion mass, the zero temperature axion mass scale for which the 21 cm forest measurements can be affected is extended further to as big as of order 10-6 eV