Associated production of a top quark with a photon via anomalous couplings

Abstract

We discuss the associated production of a top quark with a photon via anomalous t-q-γ couplings, and present higher-order corrections from soft-gluon emission for the processes gq → tγ at LHC energies. We perform soft-gluon resummation at next-to-leadinglogarithm accuracy and derive approximate next-to-next-to-leading order (aNNLO) doubledifferential cross sections. We calculate at aNNLO the total tγ production cross sections and the top-quark transverse-momentum and rapidity distributions for various LHC energies, and show that the soft-gluon corrections are large and dominant in these processes.

Three-loop soft anomalous dimensions for top-quark production

“…3.2 tZ, tZ , tγ, and tH − production Top quarks can also be produced in association with electroweak and Higgs bosons in models of new physics. Such processes include the associated production of a top quark with a charged Higgs boson via bg → tH − [21]; the associated production of a top quark with a Z boson, qg → tZ [22], or with a photon, qg → tγ [23], via anomalous couplings; and the associated production of a top quark with a Z boson either via anomalous couplings, qg → tZ , or via initial-state tops, tg → tZ [24]. The soft anomalous dimensions for all these processes are identical to the one for bg → tW − that was presented in the previous subsection.…”

$$tZ'$$ production at hadron colliders

“…The dependence of the soft function S gq→t Z on N is resummed via renormalization group evolution [30][31][32][33][34][35][36][37][38][39]43],…”

“…Therefore, the K -factors can become quite large and it is important to include these corrections in making theoretical predictions. In this study, we adopt and extend the soft-gluon resummation formalism used in [29][30][31] for t Z and tγ production (see also applications to top-antitop pair production [32][33][34] and single-top production [35][36][37][38][39], and a review in [40]) to calculate approximate next-to-nextto-leading order (aNNLO) cross sections for t Z associated production in two case scenarios: (i) the case of Z s with flavor-changing anomalous couplings, (ii) the case of Z s originating from low-energy realizations of string models. We explore the impact of the corrections due to multiple emission of soft-gluons as well as the cross section suppression due to Z s of different mass and couplings.…”

Soft anomalous dimensions for single-top production at three loops

“…The soft anomalous dimension for tW production is identical to that for other related processes in models of new physics, such as the associated production of a top quark with a charged Higgs boson via bg → tH − in two-Higgs-doublet models [27]; the associated production of a top quark with a Z boson with anomalous top-quark couplings via qg → tZ [28,29]; and the associated production of a top quark with a photon with anomalous top-quark couplings via qg → tγ [28,30]. In all these cases we have 2 → 2 processes at lowest order that involve two massless partons, a final-state top quark, and a final-state boson.…”