Dark Matter in Axion Landscape

Abstract

If there are a plethora of axions in nature, they may have a complicated potential and create an axion landscape. We study a possibility that one of the axions is so light that it is cosmologically stable, explaining the observed dark matter density. In particular we focus on a case in which two (or more) shift-symmetry breaking terms conspire to make the axion sufficiently light at the potential minimum. In this case the axion has a flat-bottomed potential. In contrast to the case in which a single cosine term dominates the potential, the axion abundance as well as its isocurvature perturbations are significantly suppressed. This allows an axion with a rather large mass to serve as dark matter without fine-tuning of the initial misalignment, and further makes higher-scale inflation to be consistent with the scenario.

23 pages, 4 figures; references added

References in corpus (7)

• Monodromy in the CMB: Gravity Waves and String Inflation
• Natural inflation with multiple sub-Planckian axions
• Tension between the power spectrum of density perturbations measured on large and small scales
• Multi-Natural Inflation in Supergravity and BICEP2
• Leptogenesis via Axion Oscillations after Inflation
• Axion Landscape and Natural Inflation
• Saving Natural Inflation

Cited by in corpus (2)

• The Spectrum of the Axion Dark Sector
• Relaxing the Cosmological Moduli Problem by Low-scale Inflation