paper

Cosmological Perturbations of Extreme Axion in the Radiation Era

arXiv:1705.01439 · doi:10.1103/PhysRevD.96.063522

Abstract

Sub-horizon perturbations under the extreme initial condition of the axion model are investigated, where initial axion angles start near the potential maximum. This work focuses on a few new features found in the extreme axion model but absent in the free-particle model. A particularly novel new feature is the spectral excess relative to the CDM model in some wave number range, where the excess may be so large that landscapes of high-redshift universe beyond can be significantly altered. For axions of particle mass eV, this range of wave number corresponds to first galaxies of few times . We demonstrate that sub-horizon perturbations are accurately described by Mathieu's equation and subject to parametric instability, which explains this novel feature. Actually the axion model is not a special one; perturbations in a wide range of scalar field models can share the similar characteristic.

arXiv comment11 pages, 3 figures

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