Abstract
Axions can be described by a relativistic field theory with a real scalar field ϕ whose self-interaction potential is a periodic function of . Low-energy axions, such as those produced in the early Universe by the vacuum misalignment mechanism, can be described more simply by a nonrelativistic effective field theory with a complex scalar field whose effective potential is a function of . We determine the coefficients in the expansion of the effective potential to fifth order in by matching low-energy axion scattering amplitudes. In order to describe a Bose-Einstein condensate of axions that is too dense to truncate the expansion of the effective potential in powers of , we develop a sequence of systematically improvable approximations to the effective potential that resum terms of all orders in .
1 More- Received 5 April 2016
DOI:https://doi.org/10.1103/PhysRevD.94.076004
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