Phenomenology of Λ _b→ Λ _{c τ} using lattice QCD calculations

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic Λ _b→ Λ _{c τ} decay. This decay is of interest in light of the R(D^(*)) puzzle in the semileptonic B¯ → D^{(∗ )} _τ 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(Λc)=ℬ[Λb→Λc]/ℬ[Λb→Λc] can strongly constrain the NP parameters of models discussed for the R(D^(*)) puzzle. We use form factors from lattice QCD to calculate all Λ _b→ Λ _{c τ} 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.