Oscillons are oscillating bound states sustained by self-interactions that appear in rather generic scalar field models. They can be extremely long-lived and 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. In this talk, we present an exploration of this idea along two different directions.
First, we provide numerical evidence for very long oscillon lifetimes in well motivated axion-like models. In particular, we focus on: potentials which grow as power-laws at large field ranges, with power 0 < p < 2; alternatively, on potentials which exhibit plateau regions at large field ranges. Second, we discuss the observational constraints on these 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.
