Part 1: I will start talking about the constraints imposed on the electromagnetic response of media by microcausality (commutators of local fields vanish outside the light cone) and positivity of the imaginary parts (the medium can only absorb energy from the external field). Modeling the medium as composed of small polarizable particles, one finds that similar positivity bounds apply to their...
We will describe the analytic structure and positivity properties of the perturbative S-matrix of excitations in a relativistic phi^4 superfluid. Motivated by this, we will then discuss how microcausality implies non-perturbative analyticity properties of correlators in a mixed (t,k) representation. This result applies to generic relativistic QFTs in homogeneous and isotropic backgrounds,...
I will discuss the extent to which thermodynamic considerations can be leveraged to derive positivity bounds on low energy effective theories.
I will explain some challenges introduced by loop corrections to gravitational EFT bounds on Wilson coefficients and how they can be overcome. Time permitting, I will show that bounds without IR divergences from massless graviton exchange can be obtained under certain reasonable assumptions.
I will discuss the EFT describing compact objects, characterized by Wilson coefficients knowns as Love numbers. I will present a method for computing this gravitational EFT to high orders and highlight the challenges involved in placing bounds on these coefficients.
