Searches of Lepton-Flavour-Violating Decays of the Higgs Boson with the ATLAS Detector at the HL-LHC

These proceedings presents a study of the prospects of searches for lepton-flavour-violating decays of the Higgs boson into $e\tau$ and $\mu\tau$ final states with $3000\,\text{fb}^{-1}$ of proton-proton collisions at $\sqrt{s} = 14\,\text{TeV}$ using the ATLAS detector at the HL-LHC. The expected HL-LHC results are estimated by extrapolating the recently published ATLAS search in the Run-2 dataset to the HL-LHC conditions, accounting for, among others, the potential reduction of uncertainties associated with particle reconstruction with the upgraded ATLAS detector, and predictions for better theoretical precision. The signatures of $H \to e\tau$ and $H \to \mu\tau$ are treated as independent signals, and two independent approaches of the background estimation are employed and compared.