Oscillons of axion-like particle: mass distribution and power spectrum

Abstract

In string theory, the simultaneous existence of many Axion-Like Particles\n(ALPs) are suggested over a vast mass range, and a variety of potentials have\nbeen developed in the context of inflation. In such potentials shallower than\nquadratic, the prominent instability can produce localized dense objects,\noscillons. Because of the approximate conservation of their adiabatic\ninvariant, oscillons generally survive quite long, maybe up to the current age\nof the universe in the case of ultra-light ALPs with $m \\sim 10^{-22}\\ {\\rm\neV}$. Such oscillons can have significant effects on the evolution of the\nrecent universe. In this paper, we investigate the oscillons of the\npure-natural type potential by classical lattice simulation to explore the key\nquantities necessary for phenomenological application: the number density of\noscillons, the oscillon mass distribution, the energy ratio of oscillons to the\nALP field, and the power spectrum. Then, we evolve these values in\nconsideration of the analytic decay rate.\n