Searches for additional Higgs bosons and for vector leptoquarks in $\tau\tau$ final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Three searches are presented for signatures of physics beyond the standard model (SM) in $\tau\tau$ final states in proton-proton collisions at the LHC, using a data sample collected with the CMS detector at $\sqrt{s} = 13\text{ TeV}$, corresponding to an integrated luminosity of $138\text{ fb}^{-1}$. Upper limits at $95\%$ confidence level ($\text{CL}$) are set on the products of the branching fraction for the decay into $\tau$ leptons and the cross sections for the production of a new boson $\phi$, in addition to the $\text{H}(125)$ boson, via gluon fusion ($gg\phi$) or in association with b quarks, ranging from $\mathcal{O}(10\text{ pb})$ for a mass of $60\text{ GeV}$ to $0.3\text{ fb}$ for a mass of $3.5\text{ TeV}$ each. The data reveal two excesses for $gg\phi$ production with local $p$-values equivalent to about three standard deviations at $m_\phi = 0.1$ and $1.2\text{ TeV}$. In a search for $t$-channel exchange of a vector leptoquark $\text{U}_{1}$, $95\%\text{ CL}$ upper limits are set on the dimensionless $\text{U}_{1}$ coupling to quarks and $\tau$ leptons ranging from $1$ for a mass of $1\text{ TeV}$ to $6$ for a mass of $5\text{ TeV}$, depending on the scenario. In the interpretation of the $M_{h}^{125}$ and $M_{h,\,\text{EFT}}^{125}$ minimal supersymmetric SM benchmark scenarios, additional Higgs bosons with masses below $350\text{ GeV}$ are excluded at $95\%\text{ CL}$.