VSI Lunch seminar, Scott Melville

Title:

UV constraints on low-energy effective theories

Abstract:

At low energies, the world around us can be described very accurately using the Standard Model and General Relativity. However, these are at best only ``effective'' descriptions: valid at low energies but destined to break down as experiments in particle physics and cosmology probe increasingly higher energies, ultimately requiring a new (UV complete) theory to take over.

In this talk, I will review the constraints which must be placed on our low-energy Effective Field Theories if they are to have any hope of a smooth Wilsonian UV completion at high energies (which is unitary, causal and local). These constraints are known as ``positivity bounds''. As two illustrative examples, I shall show how these bounds can be used to constrain Beyond the Standard Model physics (such as the dimension-8 operators in SMEFT), and also constrain theories of dark energy (such as Horndeski scalar-tensor theory). These constraints complement current and upcoming experimental data, allowing us to improve our estimation of low energy parameters.