Recipes for Oscillon Longevity

TL;DR

This paper investigates the factors influencing oscillon longevity, revealing how specific scalar potential properties and a new numerical method can extend their lifetimes to cosmological scales, impacting dark matter models.

Contribution

It introduces a novel numerical approach and clarifies how potential shape and positivity affect oscillon stability, connecting theoretical insights with potential cosmological implications.

Findings

Lifetimes of oscillons can reach up to 10^14 cycles.

Flattening and positivity of the scalar potential significantly enhance oscillon longevity.

Oscillons could be stable enough to contribute to dark matter abundance.

Abstract

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.