How a cold axion background influences photons

Abstract

A cold relic axion condensate resulting from vacuum misalignment in the early universe oscillates with a frequency \sim m_a, where m_a is the axion mass. We summarize how the properties of photons propagating in such a medium are modified. Although the effects are small due to the magnitude of the axion-photon coupling, some consequences are striking.

Comments: 4 pages, 4 figures. To appear in "Proceedings of the 7th Patras Workshop on Axions, WIMPs and WISPs"