Title: Stable, non-singular bouncing universe with only a scalar mode
I consider higher derivative, UV modifications to GR. In particular, I will focus on a specific kind of string theory-inspired higher derivative gravity where one includes derivatives to all orders in the action. I will discuss how such a non-local theory of gravity admits stable, non-singular bouncing solutions in the absence of matter. Moreover, around this bouncing background, there exists only one propagating scalar mode, and no vector or tensor modes. The scalar can be made free from ghost instabilities, and has oscillatory and bounded evolution across the bounce.