Matching between EFT and UV Complete Models

Abstract

Standard Model Effective Field Theory (SMEFT) provides an elegant mathematical framework that lets us capture imprints of new physics in a model independent way. Considering the Standard Model (SM) as a low energy approximation of a more fundamental theory allows for the addition of higher dimensional operators to the SM Lagrangian. By fitting these operators to high precision data from the Large Hadron Collider (LHC), we can simultaneously constrain a plethora of models beyond the SM (BSM). Here, information about BSM physics gets implicitly encoded in a set of Wilson coefficients. In order to extract these constraints, UV complete models need to be matched onto the SMEFT. In this thesis, we present the matching equations at tree level for a heavy scalar and a heavy vector boson in the Warsaw basis. We derive bounds for the associated couplings and masses by combining the matching equations with a SMEFT fit to LHC top quark data. As an alternative approach, we also derive bounds for the same UV parameters from an explicit BSM phenomenology analysis using differential cross sections for tt̄-production in pp-collisions at sqrt(s) = 13 TeV. Our study shows that an EFT approach is more versatile and provides sensitivity for higher energies than direct BSM searches.

As a second piece of this work, we quantify the degree to which the SMEFT fitting degrees of freedom can be constrained from top-quark processes by performing a sensitivity study. It highlights experiments that are particularly suitable to constrain SMEFT degrees of freedom.