Particle Theory Seminar | Xiaochuan Lu (University of Oregon) – Effective Field Theory for Physics Beyond the Standard Model

Seminar Organizer

Event Details

Xiaochuan Lu (University of Oregon)

In this talk, I interpret the Standard Model (SM) as a low-energy Effective Field Theory (EFT), with a particular emphasis on the indirect impact of heavy new particles. Introducing non-renormalizable interactions that preserve SM symmetries provides a robust parameterization of these effects. This well-known SMEFT framework, once truncated in mass dimension, has only a finite number of counterterms/operators, which can be systematically explored with the method of Hilbert series. With the framework established, I will discuss how to use SMEFT. When used as an interpretation of the experimental limits, global fitting results show that the current bounds are typically of a few TeV. This naturally raises a validity question regarding using SMEFT for BSM searches at the LHC which operates at a center-of-mass energy near 14 TeV. I will explain how PDF effects can sometimes salvage the validity of SMEFT. When SMEFT is used to constrain UV models, a matching and running procedure is needed to connect SMEFT with a given UV theory. Functional methods can lead to significant advantages for these calculations. Finally, I will revisit the framework and emphasize that SMEFT is not always enough — certain non-decoupling physics beyond the SM is still viable but can only be captured by the larger parameter space of the so-called Higgs EFT.