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Published April 15, 2008 | Published
Journal Article Open

Axion constraints in nonstandard thermal histories


It is usually assumed that dark matter is produced during the radiation-dominated era. There is, however, no direct evidence for radiation domination prior to big-bang nucleosynthesis. Two nonstandard thermal histories are considered. In one, the low-temperature-reheating scenario, radiation domination begins as late as ~1 MeV, and is preceded by significant entropy generation. Thermal axion relic abundances are then suppressed, and cosmological limits to axions are loosened. For reheating temperatures Trh<~35 MeV, the large-scale structure limit to the axion mass is lifted. The remaining constraint from the total density of matter is significantly relaxed. Constraints are also relaxed for higher reheating temperatures. In a kination scenario, a more modest change to cosmological axion constraints is obtained. Future possible constraints to axions and low-temperature reheating from the helium abundance and next-generation large-scale-structure surveys are discussed.

Additional Information

© 2008 The American Physical Society. (Received 8 November 2007; published 24 April 2008) D.G. was supported by the Gordon and Betty Moore Foundation and acknowledges helpful discussions with Mark Wise, Stefano Profumo, and Sean Tulin. T.L.S. and M.K. were supported by DOE No. DE-FG03-92-ER40701, NASA No. NNG05GF69G, and the Gordon and Betty Moore Foundation.

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