Bounce solutions with quantum vacuum effects of massive fields and subsequent Starobinsky inflation

Abstract: We extend the previous work about the cosmological solutions with bounce without modifications of gravity or introducing an extra scalar field. The main finding was that the bounce is possible in the initially contracting Universe filled with matter. After a strong contraction, matter gains the equation of state close to the one of radiation, such that the effect on matter on the evolution of the FLRW metric disappears at the classical level. However, this effect comes back owing to the quantum trace anomaly in the matter/radiation sector. In the present contribution, we explore the weak impact of massive fields on the anomaly-driven bounce solution and discuss the role of the vacuum terms. The masses are assumed small and regarded as small perturbations, which enables using trace anomaly even in this case. On the other hand, by adding the $R^2$ term to the action, we arrive at the model with the trans-Planckian bounce and subsequent Starobinsky inflation. In such a framework, using the numerical analysis, we consider three scenarios providing bounce solutions.