An EFT with inflaton-dependent axion kinetic term organizes direct decay and annihilation production during reheating, yielding ΔN_eff contributions that scale as T_rh^{-2} and T_rh^{4/3} respectively and allowing a two-dimensional map of constraints on Wilson coefficients and reheating temperature.
Axion constraints in non-standard thermal histories
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abstract
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 non-standard 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 less than 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.
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A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.
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An EFT Map of Axion Dark Radiation from Reheating
An EFT with inflaton-dependent axion kinetic term organizes direct decay and annihilation production during reheating, yielding ΔN_eff contributions that scale as T_rh^{-2} and T_rh^{4/3} respectively and allowing a two-dimensional map of constraints on Wilson coefficients and reheating temperature.
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Axions as Dark Matter, Dark Energy, and Dark Radiation
A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.