Classical decay rates of oscillons

Abstract

Oscillons are extremely long-lived, spatially-localized field configurations in real-valued scalar field theories that slowly lose energy via radiation of scalar waves. Before their eventual demise, oscillons can pass through (one or more) exceptionally stable field configurations where their decay rate is highly suppressed. We provide an improved calculation of the non-trivial behavior of the decay rates, and lifetimes of oscillons. In particular, our calculation correctly captures the existence (or absence) of the exceptionally long-lived states for large amplitude oscillons in a broad class of potentials, including non-polynomial potentials that flatten at large field values. The key underlying reason for the improved (by many orders of magnitude in some cases) calculation is the systematic inclusion of a spacetime-dependent effective mass term in the equation describing the radiation emitted by oscillons (in addition to a source term). Our results for the exceptionally stable configurations, decay rates, and lifetime of large amplitude oscillons (in some cases 10 8 oscillations) in such flattened potentials might be relevant for cosmological applications.

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

“…In particular, for M M P , as the field explores the flatter-than-quadratic region of the potential (φ M with α < 2), broad self-resonance drives copious production of oscillons [117,118,119,120,121,122,123]. Oscillons are highly overdense, spatially localized, exceptionally long-lived field configurations [124,125,126,127,128,129,130] where the field amplitude in their cores does not redshift as the universe expands. The rapid formation of oscillons from an almost homogeneous condensate at the end of inflation, and their slower gravitational clustering [79] is shown in Fig.…”

“…Note that oscillons are long-lived (with lifetimes ∼ 10 8 oscillations of the field[130] in some models) but not perfectly stable and will evolve by slowly emitting scalar radiation.…”

Dipole radiation and beyond from axion stars in electromagnetic fields

“…For potentials that have V (φ) ≈ (1/2)m 2 φ 2 where φ f and V (φ) ∝ φ α<2 where φ f (see figure 1), exceptionally long lived spatially localized configurations of the above form exist, and are called oscillons (setting g aγ → 0 for the moment). Typically, for very longlived oscillons, we have a field amplitude ϕ 0 ∼ f , a spatial width R ∼ few × m −1 and an oscillation frequency ω m [83]. In detail, there is a one parameter family of long lived configurations for a given potential V (φ).…”

“…This lifetime depends sensitively on the scalar potential JHEP06(2021)182 V (φ). For example, a cosine potential leads to a lifetime τ ∼ 10 3 m −1 , whereas some other potentials shown in figure 1 give much longer lifetimes τ 10 12 m −1 [83,85,86]. The formation of such oscillons from cosmological initial conditions (especially in the early universe) has been explored in detail before [87][88][89][90][91], and typically happens when H ∼ m. An almost homogeneous, oscillating condensate naturally fragments into oscillons.…”

Gravitational wave spectra from oscillon formation after inflation

“…Given the rich dynamics of non-linear field theories, we leave a detailed investigation of the properties of the produced oscillons and other localized over-densities in the various potentials that we examined for future work (for recent work on the lifetime of oscillons see refs. [27,49]). Figure 19.…”