Formation and decay of oscillons after inflation in the presence of an external coupling. Part I. Lattice simulations

Abstract We investigate the formation and decay of oscillons during the post-inflationary reheating epoch from inflaton oscillations around asymptotically flat potentials V ( φ ) in the presence of an external coupling of the form 1/2 g 2 φ 2 χ 2 . It is well-known that in the absence of such an external coupling, the attractive self-interaction term in the potential leads to the formation of copious amounts of long-lived oscillons both for symmetric and asymmetric plateau potentials. We perform a detailed numerical analysis to study the formation of oscillons in the α -attractor E- and T-model potentials using the publicly available lattice simulation code C osmo L attice. We observe the formation of nonlinear oscillon-like structures with the average equation of state ⟨ w φ ⟩ ≃ 0 for a range of values of the inflaton self-coupling λ and the external coupling g 2 . Our results demonstrate that oscillons form even in the presence of an external coupling and we determine the upper bound on g 2 which facilitates oscillon formation. We also find that eventually, these oscillons decay into the scalar inflaton radiation as well as into the quanta of the offspring field χ . Thus, we establish the possibility that reheating could have proceeded through the channel of oscillon decay, along with the usual decay of the oscillating inflaton condensate into χ particles. For a given value of the self-coupling λ , we notice that the lifetime of a population of oscillons decreases with an increase in the strength of the external coupling, following an (approximately) inverse power-law dependence on g 2 .