Cosmological implications of axion

Abstract

We discussed the cosmological role of the ALP conversion physics such as coherent oscillation, resonant conversion, and tachyonic instability. We showed that by introducing dark photon coupling and background dark magnetic field, spectral modulations in some galactic pulsars can be explained without conflict with existing astrophysical and cosmological constraints. We also discussed how such coupling can alleviate the CMB constraint on resonant photon conversion and studied its implication. Dark magnetic field generation mechanism with tachyonic instability and application to the cosmological constant problem is presented.