Oscillons and Dark Matter
  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.
