ITMP Seminar "Stability of nonsingular Cosmologies in Galileons with Torsion"

Abstract: Horndeski theory, also known as Galileons, is a modification of General Relativity by a scalar field, with higher derivatives in the action but with second order equations of motion. It has been widely studied in part due to the possibility to violate the null energy condition and to construct interesting cosmological solutions. In this talk we introduce Galileons on a spacetime with torsion and discuss the implications for the stability of the FLRW background against the graviton and the scalar mode. The main point is a critical modification of a well known No-Go theorem that holds for nonsingular cosmological solutions in the torsionless theory (up to some special cases). The talk is based on our recent studies: 2304.04722 and 2307.06929.