Search

I discuss how modified EW interactions lead to energy growth in $2\to 2$ scattering amplitudes and how the framework of the Standard Model Effective Field Theory can be used in conjunction with the Goldstone boson equivalence theorem to better understand the origin of such unitarity violating behaviour. I quantify how applications in constraining top quark electroweak couplings are especially motivated due to our relatively poor understanding of them. I present some highlights of a systematic study of energy growth in EW top scattering amplitudes with a focus on how such effects can be searched for in realistic collider processes, demonstrating some promising avenues for future study., Comment: 7 pages, 3 figures. Contribution to the 2021 EW session of the 55th Rencontres de Moriond

In the context of the Standard Model effective field theory (SMEFT), we study the LHC sensitivity to four fermion operators involving heavy quarks by employing cross section measurements in the $t\bar{t}b\bar{b}$ final state. Starting from the measurement of total rates, we progressively exploit kinematical information and machine learning techniques to optimize the projected sensitivity at the end of Run III. Indeed, in final states with high multiplicity containing inter-correlated kinematical information, multi-variate methods provide a robust way of isolating the regions of phase space where the SMEFT contribution is enhanced. We also show that training for multiple output classes allows for the discrimination between operators mediating the production of tops in different helicity states. Our projected sensitivities not only constrain a host of new directions in the SMEFT parameter space but also improve on existing limits demonstrating that, on one hand, $t\bar{t}b\bar{b}$ production is an indispensable component in a future global fit for top quark interactions in the SMEFT, and on the other, multi-class machine learning algorithms can be a valuable tool for interpreting LHC data in this framework., Comment: 47 pages, 18 figures, 3 tables, Restructured the sections, expanded discussion on SMEFT operators in ttbb, EFT validity & power-counting and methodology. References added. 1 new figure. Version accepted by JHEP

We propose a procedure to cross-validate Monte Carlo implementations of the standard model effective field theory. It is based on the numerical comparison of squared amplitudes computed at specific phase-space and parameter points in pairs of implementations. Interactions are fully linearised in the effective field theory expansion. The squares of linear effective field theory amplitudes and their interference with standard-model contributions are compared separately. Such pairwise comparisons are primarily performed at tree level and a possible extension to the one-loop level is also briefly considered. We list the current standard model effective field theory implementations and the comparisons performed to date., agreement achieved under the auspices of the LHC Top and Electroweak Working Groups, and of the LHC Higgs Cross Section Working Group