The present and future of four top operators

Abstract

We study the phenomenology of a strongly-interacting top quark at future hadron and lepton colliders, showing that the characteristic four-top contact operators give rise to the most significant effects. We demonstrate the extraordinary potential of a 100 TeV proton-proton collider to directly test such non-standard interactions in four-top production, a process that we thoroughly analyze in the same-sign dilepton and trilepton channels, and explore in the fully hadronic channel. Furthermore, high-energy electron-positron colliders, such as CLIC or the ILC, are shown to exhibit an indirect yet remarkable sensitivity to four-top operators, since these constitute, via renormalization group evolution, the leading new-physics deformations in top-quark pair production. We investigate the impact of our results on the parameter space of composite Higgs models with a strongly-coupled (right-handed) top quark, finding that four-top probes provide the best sensitivity on the compositeness scale at the future energy frontier. In addition, we investigate mild yet persisting LHC excesses in multilepton plus jets final states, showing that they can be consistently described in the effective field theory of such a new-physics scenario.

Top, Higgs, diboson and electroweak fit to the Standard Model effective field theory

“…Finally, we also omit the four-heavy operators that would mainly be constrained by ttbb measurements and four-top production searches. These data have been shown to be largely sensitive, at present, to the quadratic EFT contributions [168,[190][191][192], and our analysis would not yield meaningful bounds in these directions. We therefore only include in our analysis 8 two-heavy two-light quark degrees of freedom: the colour-singlet, charged-current operator and seven neutral, colour-octet operators.…”

“…The higher energies at the LHC also allow certain measurements of diboson and dilepton final states to become competitive with LEP [126,[185][186][187][188][189]196], enable complementary probes of higher-dimensional operators [111,197], and, moreover, give access to top physics with higher statistics than ever before, including the previously unreachable ttW/Z/H and other, rare production processes such as four-top production [168,[190][191][192]. More operators, under less restrictive flavour assumptions, can then be included in a global SMEFT fit.…”

The flavor of UV physics

“…Probing flavor universality breaking at the LHC requires adding observables that probe four-quark operators through light quarks or through top quarks only. For instance, adding four-top production [102,103] and/or dijet production [104] to the top fit would allow us to distinguish between flavor-universal and flavor-breaking four-quark interactions. These are interesting directions for future work, especially in the context of the current discrepancies in b → s + − observables.…”

Top-philic heavy resonances in four-top final states and their EFT interpretation

“…with a mass below the top mass m t , has been studied in the past [35], and an emphasis has been put on the associated production of such particles with a top quark pair [36]. Several phenomenological studies have appeared recently with the goal to bound new physics contributions in four top-quark production in the Standard Model Effective Field Theory (SMEFT) framework [37][38][39][40][41][42][43][44][45][46]. While powerful, the SMEFT approach has also intrinsic limitations that could become relevant in the four-top production case.…”