The top threshold effect in the γγ production at the LHC

We compute the top quark threshold contributions to the $\gamma\gamma$ production at the LHC. They appear when the invariant mass of the photon pair, $M_{\gamma\gamma}$ just exceeds two times the mass of the top quark and induce some feature in the $M_{\gamma\gamma}$ distribution. We determine the magnitude of this threshold effect and characterize this feature with a simple empirical fitting function to show that it is possible to observe this effect at the LHC in future. We also explore some possible improvements that may enhance its significance.