Abstract
Real scalar fields with attractive self-interaction may form self-bound states, called oscillons. These dense objects are ubiquitous in leading theories of dark matter and inflation; of particular interest are long-lived oscillons which survive past $14$ Gyr, offering dramatic astrophysical signatures into the present day. We introduce a new formalism for computing the properties of oscillons with improved accuracy, which we apply to study the internal structure of oscillons and to identify the physical mechanisms responsible for oscillon longevity. In particular, we show how imposing realistic boundary conditions naturally selects a near-minimally radiating solution, and how oscillon longevity arises from its geometry. Further, we introduce a natural vocabulary for the issue of oscillon stability, which we use to predict new features in oscillon evolution. This framework allows for new efficient algorithms, which we use to address questions of whether and to what extent long-lived oscillons are fine-tuned. Finally, we construct a family of potentials supporting ultra-long-lived oscillons, with lifetimes in excess of $10^{17}$ years.
Highlights
Axions are real scalar fields predicted to exist in many extensions of the Standard Model
Understanding oscillon lifetime is necessary for determining whether oscillons only play a role in early Universe cosmology or whether they may survive until the present day and lead to dramatic astrophysical signatures
We defined the physical quasibreather by finding initial conditions of the nonlinear wave equation that simultaneously obey radiative boundary conditions and specify a quasibreather solution
Summary
Axions are real scalar fields predicted to exist in many extensions of the Standard Model. We apply our new methods to systematically study oscillon lifetimes in periodic axion potentials, allowing us to probe the genericity of long-lived oscillons. Geometric decoupling.—The size of the oscillon is ipnvffiffieffiffirffiffisffiffieffiffilffiyffiffiffipffiffiroportional to the binding energy per particle m2 − ω2, which blows up as ω approaches the rest mass m (see Fig. 4) In this limit, the oscillon grows much larger than the wavelengths of radiation 2π=nω, causing a separation of scales. At frequencies ω approaching the mass m, there is a point past which an external energy source is necessary for the oscillon to remain bound At this point, the oscillon is forced to undergo a rapid process of dissipation, which we call energetic death.
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