Electromagnetic waves propagating in the string axiverse

Understand

It is widely believed that axions are ubiquitous in string theory and could be the dark matter.

• The peculiar features of the axion dark matter are coherent oscillations and a coupling to the electromagnetic field through the Chern-Simons term.
• In this paper, we study consequences of these two features of the axion with the mass in a range from $10^{-13}\,{\rm eV}$ to $10^{3}\,{\rm eV}$.
• First, we study the parametric resonance of electromagnetic waves induced by the coherent oscillation of the axion.