Tensor bounds on the hidden universe (and a 1PI coda on loops in inflation)

by Subodh Patil (NBIA)

Monday 17 Feb 2020, 13:15 → 14:15 Europe/Stockholm

132:028 (Nordita East)

In this talk, we present the observation that primordial gravitational waves, if ever observed, can be used to bound
the hidden field content of the universe. This is because a large number of hidden fields can resum to potentially observable logarithmic runnings for the graviton two-point function in the context of single field inflation, courtesy of a `large N' resummation.  This allows one to translate ever more precise bounds on the so-called tensor to scalar consistency relation into bounds on the hidden field content of the universe, with potential implications for phenomenological constructions that address naturalness with a large number of species. Along the way, we need to address certain subtleties regarding loop corrections on cosmological backgrounds, especially with regards to the correct implementation of dimensional regularization. We find a pleasing confirmation of our understanding by directly reproducing our results from the 1PI effective action, and present a simplified prescription to calculate loop corrections to certain correlation functions in inflation, drawing a line under a long standing debate in the literature.