Search for singly and pair-produced leptoquarks coupling to third-generation fermions in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for leptoquarks produced singly and in pairs in proton-proton collisions is presented. The leptoquark (LQ) may couple to a top quark plus a $\tau$ lepton (t$\tau$) or a bottom quark plus a neutrino (b$\nu$, scalar LQ), or else to t$\nu$ or b$\tau$ (vector LQ), leading to the final states t$\tau\nu$b and t$\tau\nu$. The data were recorded by the CMS experiment at the CERN LHC at $\sqrt{s}$ = 13 TeV and correspond to an integrated luminosity of 137 fb$^{-1}$. The data are found to be in agreement with the standard model background prediction. Lower limits at 95$\%$ CL are set on the LQ mass in the range 0.98-1.73 TeV, depending on the LQ spin and the LQ-lepton-quark vertex coupling $\lambda$, and assuming equal branching fractions for the two LQ decay modes considered. These are the most stringent constraints on the existence of leptoquarks in this scenario.