Oscillon Formation in Palatini Modified Gravity Theories

Abstract: We investigate the formation of spatially localized, oscillatory in time and non topological solitonic, quasi-stable energy configurations, Oscillons, which are formed at the end of Inflationary epoch, during the preheating phase and decay over long periods of time. Oscillons have been previously studied in literature in the regime of General Relativity using Metric Formalism. In this paper we look for formation of these energy lumps by modifying the gravity part of the Einstein Hilbert Action, considering a non minimal coupling of the scalar field with Ricci Scalar,$R$, and working in an alternative formulation of General Relativity known as Palatini Formalism. The potential we consider is of polynomial form. We demonstrate numerically, using CosmoLattice, that the equation governing the dynamics of the Inflaton scalar field give oscillatory and decaying solutions as it is expected in the case of Oscillons, with power spectrum governing the growth of perturbations of $k$ modes. The equation of state reveals an extended period of Oscillon domination in the early universe. Along with this, the Primordial Gravitational Wave spectrum due to asymmetric distribution of these energy configurations have also been studied. We observe that these generate Ultra-High Frequency regime Gravitational Waves, which lie in the range of the planned future detectors and experiments.