HET Journal club: Spyridon Talaganis

(Note unusual time: 11:15)

Speaker: Spyridon Talaganis (Lancaster University)

Title: Ultraviolet Behavior & High-Energy Scatterings in Infinite-Derivative Theories of Gravity

Abstract: In this talk, I will consider the ultraviolet behavior of quantum loops & scattering diagrams in the context of infinite-derivative theories. The graviton propagator in this theory gets an exponential suppression making it asymptotically free, thus providing strong prospects of resolving various classical and quantum divergences. In particular, we will find that at 1-loop, the 2-point function is still divergent, but once this amplitude is renormalized by adding appropriate counter terms, the ultraviolet (UV) behavior of all other 1-loop diagrams as well as the 2-loop, 2-point function remains well under control. We will go on to discuss how one may be able to generalize our computations and arguments to arbitrary loops. Then, I examine a finite-order, higher-derivative scalar field theory and find that one cannot eliminate the growth of scattering diagrams for large external momenta. Consequently, I employ an infinite-derivative scalar toy model and obtain that the external momentum dependence of scattering diagrams is convergent as the external momenta become very large. In order to eliminate the external momentum growth, one has to dress the bare vertices of the scattering diagrams by considering renormalized propagator and vertex loop corrections to the bare vertices. Finally, I investigate scattering diagrams in the context of a scalar toy model which is inspired by a ghost-free and singularity-free infinite-derivative theory of gravity, where I conclude that infinite derivatives can eliminate the external momentum growth of scattering diagrams and make the scattering diagrams convergent in the ultraviolet.