Ephemeral Oscillons in Scalar-Tensor Theories: The Higgs-like case (2501.14869v2)

Abstract: We investigate the post-inflationary evolution of a non-minimally coupled inflaton field in scalar-tensor theories, framed within the flexible framework of Einstein-Cartan gravity. By focusing on a class of simplified Higgs-like scenarios, we simulate the transition from the end of inflation to the formation of oscillons using fully-fledged 3+1 classical lattice simulations. Once oscillons form, we extract their profiles and perform 1+1 simulations to evolve their radial equations. Our findings reveal that these oscillons, unlike typical cases in the literature, are relatively short-lived, due to the presence of self interactions at small field values. The radiation produced by this novel type of oscillons can quickly lead to a radiation-dominated Universe, even in the absence of additional fields or interactions. Finally, we leverage our results to derive precise predictions for the inflationary observables and the produced spectrum of gravitational waves associated with oscillon formation. Significantly, our study establishes also an upper bound on the duration of the heating phase in Einstein-Cartan Higgs inflation scenarios.