# Oscillons and Dark Matter

## TL;DR

Oscillons, long-lived scalar bound states formed via parametric resonance, could significantly influence ultra-light dark matter models by acting as early structure seeds or surviving as dark matter today.

## Contribution

This paper investigates the lifetimes of oscillons in axion-like models and explores their potential role as dark matter or early universe structure seeds.

## Key findings

- Oscillons can live up to 10^8 cycles depending on the potential shape.
- Oscillons decay around or after matter-radiation equality, affecting structure formation.
- Possibility of oscillons surviving to the present day as dark matter.

## Abstract

Oscillons are bound states sustained by self-interactions that appear in rather generic scalar models. They can be extremely long-lived and in the context of cosmology they have a built-in formation mechanism - parametric resonance instability. These features suggest that oscillons can affect the standard picture of scalar ultra-light dark matter (ULDM) models. We explore this idea along two directions. First, we investigate numerically oscillon lifetimes and their dependence on the shape of the potential. We find that scalar potentials that occur in well motivated axion-like models can lead to oscillons that live up to $10^8$ cycles or more. Second, we discuss the observational constraints on the ULDM models once the presence of oscillons is taken into account. For a wide range of axion masses, oscillons decay around or after matter-radiation equality and can thus act as early seeds for structure formation. We also discuss the possibility that oscillons survive up to today. In this case they can most easily play the role of dark matter.