Phenomenology of Λ b → Λ c τ ν ¯ τ b c using lattice QCD calculations

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic b c decay. This decay is of interest in light of the R (D (*) ) puzzle in the semileptonic B D^ () decays. In this work we add tensor operators to extend our previous results and consider both model-independent new physics (NP) and specific classes of models proposed to address the R (D (*) ) puzzle. We show that a measurement of R (c) =Bb c _/Bb c _ can strongly constrain the NP parameters of models discussed for the R (D (*) ) puzzle. We use form factors from lattice QCD to calculate all b c observables. The Λ b → Λ c tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.