Recipes for oscillon longevity

Oscillons are localized states of scalar fields sustained by self interactions. They decay by emitting classical radiation, but their lifetimes are surprisingly large. We revisit the reasons behind their longevity, aiming at how the shape of the scalar potential V (phi) determines the lifetime. The corpuscular picture, where the oscillon is identified with a bound state of a large number of field quanta, allows to understand lifetimes of order of 10(3) cycles in generic potentials. At the non-perturbative level, two properties of the scalar potential can substantially boost the lifetime: the flattening of V (phi) and the positivity of V'' (phi). These properties are realized in the axion monodromy family of potentials. Moreover, this class of models connects continuously with an exceptional potential that admits eternal oscillon solutions. We check these results with a new fast-forward numerical method that allows to evolve in time to stages that cannot be otherwise simulated on a computer. The method exploits the attractor properties of the oscillons and fully accounts for nonlinearities. We find lifetimes up to 10(14) cycles, but larger values are possible. Our work shows that oscillons formed in the early Universe can be stable on cosmological time scales and thus contribute to the abundance of (ultra)light scalar dark matter.

Automated summary

Oscillons are localized states of scalar fields sustained by self interactions with surprisingly long lifetimes. The shape of the scalar potential and two properties, the flattening of V (phi) and the positivity of V'' (phi), can substantially boost the lifetime, with potential eternal oscillon solutions in some cases. The study shows that oscillons formed in the early Universe can be stable on cosmological time scales, contributing to the abundance of (ultra)light scalar dark matter.