On the coupling of axion-like particles to the top quark

Abstract

In this paper we explore the coupling of a light axion-like particle (ALP) to top quarks. We use high-energy LHC probes, and examine both the direct probe to this coupling in associated production of a top-pair with an ALP, and the indirect probe through loop-induced gluon fusion to an ALP leading to top pairs. Using the latest LHC Run II data, we provide the best limit on this coupling. We also compare these limits with those obtained from loop-induced couplings in diboson final states, finding that the $$ t\overline{t} $$ t t ¯ +MET channel is the best current handle on this coupling.

Top Secrets: long-lived ALPs in top production

“…refs. [29,30]. The decays of these and similar light top-philic particles are loop-suppressed, leading to a long decay length.…”

“…In ref. [30], the authors have re-interpreted an ATLAS search for top-pairs and missing energy [68] for detector-stable ALPs in a broader mass range (see also ref. [69]).…”

“…Missing energy and displaced vertex searches therefore probe complementary mass regimes of ALPs with top couplings. Alternatively, the ALP-top coupling can be probed indirectly through NLO effects in t t production [30,70]. The sensitivity is comparable to top-associated missing energy searches.…”

“…At the LHC, effective ALP couplings to photons, weak gauge bosons, and the Higgs can be probed in, for instance, di-boson production and h → Za decays [72][73][74]. In the top scenario, the derived indirect bounds on the ALP-top coupling range around |c tt |/f a ≲ 10−100/TeV at 95% CL [30]. With the current experimental status, the sensitivity to the ALP coupling to virtual tops is weaker than in searches with resonant tops.…”

FIMP Dark Matter at the LHC

“…Much explored are Higgs decays, which are very sensitive to ALP couplings to the Higgs boson, but also to the top quark and weak gauge bosons through loop-induced decays [6]. Alternatively, ALPs can be produced from resonant top quarks, for instance in association with a top-antitop pair [7][8][9][10]. For long decay lengths, a displaced di-lepton vertex in association with a top-antitop pair is a promising signature [8].…”