Search for dark matter in events with a Higgs boson decaying to two photons and missing transverse momentum in pp collisions at √s = 13 TeV with the ATLAS detector

A dark matter search in the events with a Higgs boson decaying to two photons and missing transverse momentum is performed. The $139~\mathrm{fb}^{-1}$ of proton-proton collision data collected at the centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN LHC between the years 2015 and 2018 is used in this study. The results are interpreted in a simplified model with a massive vector mediator that emits a Higgs boson and subsequently decays into a pair of dark matter candidates, and in a two-Higgs-doublet model with either a vector or a pseudoscalar mediator to a pair of dark matter candidates. No significant excess beyond the Standard Model is observed.