G-bounce

Abstract

We present a wide class of models which realise a bounce in a spatially flat\nFriedmann universe in standard General Relativity. The key ingredient of the\ntheories we consider is a noncanonical, minimally coupled scalar field\nbelonging to the class of theories with Kinetic Gravity Braiding /\nGalileon-like self-couplings. In these models, the universe smoothly evolves\nfrom contraction to expansion, suffering neither from ghosts nor gradient\ninstabilities around the turning point. The end-point of the evolution can be a\nstandard radiation-domination era or an inflationary phase. We formulate\nnecessary restrictions for Lagrangians needed to obtain a healthy bounce and\nillustrate our results with phase portraits for simple systems including the\nrecently proposed Galilean Genesis scenario.\n