Hybrid nonsingular solutions of the Einstein-Gauss-Bonnet model

Abstract

The standard cosmological model, based on the concept of the Big Bang, inevitably faces the problem of an initial singularity, in which modern physical laws lose their applicability. One of the alternative approaches to solving this problem is the theory of cosmological bounce, which assumes a phase of contraction preceding the expansion of the Universe. However, traditional bounce models often conflict with inflationary theory and can lead to dynamic instabilities.  This paper presents a new model of cosmological bounce based on modified Einstein-Gauss-Bonnet gravity and using a hybrid type scale factor combining the advantages of power and exponential expansion. To verify the correspondence of the model to the observational data, the Markov chain Monte Carlo method was applied using Pantheon+ and SH0ES datasets. It is shown that the proposed model has dynamic stability, confirmed by positive values of the propagation speed of baryon oscillations, and provides a smooth transition from decelerated expansion to accelerated expansion.  The analysis of the early stages of the Universe's evolution was carried out based on slow-roll parameters, demonstrating the presence of an inflationary phase and its sufficient duration for subsequent expansion. Additional verification of the model was carried out by comparing theoretical predictions with Planck 2018 observational data processed using the Cobaya statistical code. The results obtained confirm the possibility of realizing a stable cosmological rebound consistent with the inflationary paradigm and modern cosmological constraints.