Gauss–Bonnet Inflation after Planck2018

Abstract

Abstract We study the primordial perturbations and reheating process in the models where the Gauss–Bonnet (GB) term is nonminimally coupled to the canonical and noncanonical (DBI and tachyon) scalar fields. We consider several potentials and GB coupling terms as power-law, dilaton-like, cosh-type, E-model, and T-model. To seek the observational viability of these models, we study the scalar perturbations numerically and compare the results with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at 68% CL and 95% CL. We also study the tensor perturbations in confrontation with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO, and Virgo2016 joint data at 68% CL and 95% CL. In this regard, we obtain some constraints on the GB coupling parameter β. Another important process in the early universe is the reheating phase after inflation, which is necessary to reheat the universe for subsequent evolution. In this regard, we study the reheating process in these models and find some expressions for the e-folds number and temperature during that era. Considering that from Planck TT, TE, EE+lowEB+lensing data and BICEP2/Keck Array 2014, based on the ΛCDM model, we have n s = 0.9658 ± 0.0038 and r < 0.072, we obtain some constraints on the e-folds number and temperature. From the values of the e-folds number and the effective equation of state and also the observationally viable value of the scalar spectral index, we explore the capability of the models in explaining the reheating phase.