Search for Higgs boson pair production and constraints on Higgs couplings in the $b\overline{b}{\tau }^{+}{\tau }^{-}$ final state with 36.1 fb${}^{-1}$ of pp collisions data at $\sqrt{s}$ = 13 TeV with the ATLAS detector

In the SM Higgs boson pairs can be produced via gluon-gluon fusion through top-quark loops and the Higgs triple self-interaction. The study of this process can therefore allow to probe the structure of the Higgs potential by measuring the Higgs self-coupling ${\lambda }_{HHH}$. Although the SM cross-section for Higgs pair production is very small, modifications to the top-quark Yukawa coupling or to the Higgs self-coupling, could enhance the di-Higgs production rate and show hints of possible new physics in this process. It is therefore interesting to set constraints on these couplings with the 2015+2016 dataset collected by ATLAS even without yet having the sensitivity to observe the SM process. Moreover, many BSM theories predict heavy resonances that could decay into a pair of Higgs bosons, such as a neutral scalar heavy Higgs in two-Higgs doublet models or spin-2 Kaluza-Klein excitations of the graviton in the bulk Randall-Sundrum model. In the assumption of SM Higgs bosons with m=125 GeV, the $b\overline{b}{\tau }^{+}{\tau }^{-}$ channel of the di-Higgs decay has the third largest branching fraction (7.4%). The results of the search for Higgs boson pair production in the $b\overline{b}{\tau }^{+}{\tau }^{-}$ final state obtained with 36.1 fb${}^{-1}$ of pp collisions data at $\sqrt{s}$ = 13 TeV with the ATLAS detector will be presented in this talk.