[HET seminar] Effective Field Theory for Physics Beyond the Standard Model

by Xiaochuan Lu (University of Oregon)

Thursday 14 Oct 2021, 11:00 → 13:00 US/Eastern

https://bnl.zoomgov.com/j/1612154637?pwd=Z2E5RWhqRXBkMnExQzc3eVBTWTg3UT09

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 Beyond the SM effects. Once this expansion is truncated, SMEFT has only a finite number of counterterms/operators, making it well defined. This approach 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 validty of SMEFT, even in this parameter space where a parton level analysis would suggest it is not a useful description. 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. It is also interesting to consider imposing further symmetries/constraints on SMEFT to reduce the number of degrees of freedom, which is apt for certain classes of BSM physics. Finally, I will revisit the framework and emphasize that SMEFT is not always enough --- certain non-decoupling BSM physics is still viable but can only be captured by the larger parameter space of the so-called Higgs EFT.

SMEFT_BNL_2021-10-14.pdf