New Target for Cosmic Axion Searches.
Future cosmic microwave background experiments have the potential to probe the density of relativistic species at the subpercent level. This sensitivity allows light thermal relics to be detected up to arbitrarily high decoupling temperatures. Conversely, the absence of a detection would require extra light species never to have been in equilibrium with the Standard Model. In this Letter, we exploit this feature to demonstrate the sensitivity of future cosmological observations to the couplings of axions to photons, gluons, and charged fermions. In many cases, the constraints achievable from cosmology will surpass existing bounds from laboratory experiments and astrophysical observations by orders of magnitude.
DAMTP, University of Cambridge, Cambridge, CB3 0WA, United Kingdom.|IoP, University of Amsterdam, Amsterdam, 1090 GL, Netherlands.
Daniel
D
Baumann
Department of Physics, University of California, Berkeley, CA 94720, USA.|Canadian Institute for Theoretical Astrophysics, Toronto, ON M5S 3H8, Canada.
Daniel
D
Green
DAMTP, University of Cambridge, Cambridge, CB3 0WA, United Kingdom.
Benjamin
B
Wallisch