Probing new physics in top-quark pair production in association with a photon and triple-top signal at the LHC

In this paper, we present a detailed study to probe top-quark flavor changing neutral current (FCNC) interactions at , , and vertices with top-quark pair in association with a photon and three-top-quarks signal at the Large Hadron Collider (LHC). We investigate the top-quark FCNC couplings and carry out a full simulation for the triple-top production considering the main backgrounds. In addition, having at hand the cross section of a top-quark pair produced in association with a photon in collisions at a centre-of-mass energy of 8 TeV with 20.2 of data collected by the ATLAS detector, we also investigated the FCNC coupling. The obtained exclusion limits on coupling strengths and branching ratios are summarized and compared with the results in literature. The discovery potential for anomalous couplings , , and with an integrated luminosity of are also examined in detail. We show that, for higher luminosities within Run-II of LHC, a dedicated search for the top-quark FCNC couplings can achieve comparable or even better sensitivities to the triple-top signal than the other top-quark production scenarios. We have shown that the triple-top signal could potentially provide evidence for new physics at the LHC.