Constraining four-fermion operators using rare top decays

TL;DR

This paper uses LHC data on rare top decays to set bounds on four-fermion operators, improving constraints over previous methods and exploring implications for ultraviolet complete models.

Contribution

It provides new bounds on four-fermion operators from rare top decays and assesses their impact on specific ultraviolet models.

Findings

LHC bounds surpass flavor physics constraints in certain cases

Prospects for high-luminosity LHC to further constrain operators

Identification of ultraviolet completions inducing these operators

Abstract

New physics can manifest itself by an appreciable increase of the decay rate of top quarks in rare flavour-changing final states. Exploiting the large top quark production rate at the LHC, we bound four-fermion operators contributing to non-resonant $t\rightarrow \ell^+\ell^- j$ using different signal regions of the latest LHC searches for $t\rightarrow Zj$. We also provide prospects for the high-luminosity LHC to test these as well as four-fermion operators contributing to $t\rightarrow b\overline{b}j$, based on improved analysis strategies of existing searches. We single out all weakly-coupled ultraviolet completions inducing such contact interactions at tree level and translate the previous bounds to the parameter space of specific complete models. Being above the TeV, LHC bounds from rare top decays improve over those from flavour physics, electroweak precision data and other LHC searches in several cases.