Searching for BSM Physics in Yukawa Couplings and Flavour Symmetries

TL;DR

This paper investigates bounds on new physics affecting Yukawa couplings within the Standard Model Effective Field Theory, comparing collider and flavor-changing neutral current data under different flavor symmetry assumptions, revealing current constraints and future prospects.

Contribution

It provides a comprehensive global analysis of bounds on new physics scales from Higgs and flavor observables considering specific flavor structures, highlighting the relative strength of collider versus flavor constraints.

Findings

FCNC data impose stronger bounds than collider data for leptons.

Bounds are in the TeV range, compatible with small deviations from SM Yukawas.

Future collider signals could indicate flavor symmetry violation or additional BSM effects.

Abstract

In the framework of the Standard Model Effective Field Theory, we compare the lower bounds on the scale of new physics possibly contributing to the $f\bar{f}h$ effective couplings, obtained from the measurements of different observables, under the assumption that the Wilson coefficients of the relevant dim 6 operators respect certain flavour structure: either the Minimal Flavour Violation (MFV) ansatz or a flavour symmetry, often invoked to explain the observed pattern of fermion masses and mixings. We perform a global analysis of the bounds following from the limits on the diagonal couplings measured in the Higgs boson production and decays at the LHC experiments. Another set of bounds is obtained from the limits on non-diagonal couplings constrained by the variety of flavour changing neutral current (FCNC) and radiative decay processes. With the present precision of the LHC data, the FCNC data give stronger bounds on the scale of new physics than the collider data (obviously, for the MFV ansatz only collider data are relevant): once the Wilson coefficients respect some flavour structure, the obtained bounds are in the TeV range. In the quark case, these limits are compatible with a few percent deviations from the SM Yukawa couplings and only mildly more stringent than those obtained from the available collider data. For leptons, instead, the FCNC bounds are stronger and then a signal in the near future collider data would mean the violation of the flavour symmetry or indicate the presence of additional beyond the Standard Model contributions, affecting the flavour observables, that leads to cancellations.