# High Energy Physics Seminar

Monday, May 3, 2021
10:00am to 11:00am
Online Event
Beyond Lorentz's Lamp-post: Positivity Bounds for Cosmology
Scott Melville, DAMTP, University of Cambridge,

Note: special time.

When searching for new fundamental physics, Effective Field Theory (EFT) is often the framework of choice, since it provides a useful parametrisation of the low-energy phenomenology which can be readily compared with data.

However, not all low-energy EFTs are physical - in particular, basic requirements such as unitarity and causality of the underlying UV physics place tight constraints on the low-energy EFT parameters, known as positivity bounds''.

Implementing these bounds is crucial if we are to extract UV information from our low-energy measurements, but much of the progress to date has been confined to Lorentz-invariant systems.

In this talk, I will describe how to extend positivity bounds to systems without Lorentz symmetry in order to identify the physical EFTs for cosmology or condensed matter systems (in which Lorentz symmetry is spontaneously broken).

For the Effective Field of Theory of inflation, these new bounds identify a region of parameter space in which unitarity/causality guarantees new physics beyond single-field, weakly coupled inflation.