Misalignment vs Topology in Axion-Like Models

Abstract

Cosmological axions, an important dark matter candidate, are generated when a scalar field with a spontaneously broken O(2) invariance develops an explicitly O(2)-breaking tilt cosmologically, leading to coherent production of long-wavelength modes which could be dark matter. It appears that the production efficiency of this mechanism is low, despite possible production from topological structures. To understand this better, we examine production in O(N) generalizations. In particular we highlight the importance of how fast the explicit O(N)-breaking potential turns on.