Oscillons

Oscillons are localized, oscillating solutions of the classical equations of motion for real scalar fields in nonlinear potentials. They are non-topological, time-dependent field configurations that remain spatially confined for long times, behaving like particle-like objects in field theory.

They arise in theories with attractive self-interactions or nontrivial potentials, such as polynomial or periodic forms, where nonlinearities balance dispersion to produce a localized lump. An oscillon does not correspond to a stable static solution; instead it is a quasi-stable configuration that slowly emits radiation, allowing it to persist for many oscillation periods before eventually decaying.

Formation and occurrence: Oscillons can form from generic initial conditions in early-universe cosmology, particularly during preheating and fragmentation of the inflaton or other scalar condensates. They also appear in simulations of axion-like fields or other real scalar models. Their existence has been demonstrated primarily through numerical studies, with analytic approaches providing insight into the mechanisms that suppress fast decay.

Properties and dynamics: The core oscillates at a frequency typically below the mass scale of the scalar field, reducing radiation into elementary quanta. The energy is concentrated in a localized region, and the size is set by the balance of nonlinear and gradient terms. In two and three spatial dimensions, oscillons can be long-lived, though their lifetimes are finite and depend on the potential, amplitude, and dimensionality. Decay proceeds via emission of small-amplitude waves and gradual energy loss.

Relation to other solitons: Oscillons are distinct from topological solitons and from Q-balls, which carry a conserved global charge. They are a topic of active research due to their potential implications for early-universe dynamics and gravitational-wave production.