Probing the top-Higgs boson FCNC couplings via the h → γγ channel at the HE-LHC and FCC-hh

We investigate the sensitivity of future searches for the top-Higgs boson flavor changing neutral current (FCNC) couplings tqh (q = u, c) at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in the hadron-hadron mode (FCC-hh). We perform a full simulation for the two processes in the h -> gamma gamma decay channel (where h is the discovered Higgs boson state): the single top quark FCNC production in association with the Higgs boson (plus a jet) and the top quark pair production with FCNC decays t -> qh. All the relevant backgrounds are considered in a cut based analysis to obtain the limits on the branching ratios (BRs) of t -> uh and t -> ch. It is shown that, at the HE-LHC with an integrated luminosity of 15 ab(-1) and at the FCC-hh with an integrated luminosity of 30 ab(-1), the BR(t -> uh) [BR(t -> ch)] can be probed, respectively, to 7.0(8.5) x 10(-5) and 2.3(3.0) x 10(-5) at the 95% confidence level (C.L.) (assuming a 10% systematic uncertainty on the background), which is almost 2 orders of magnitude better than the current 13 TeV LHC experimental results.