$Λ_b \to (Λ_c,\,p)\,τ\,ν$ decays within standard model and beyond

Deviations from the standard model prediction have been observed in several leptonic and semileptonic $B$ meson decays to $τν$ final states mediated via $b \to u$ and $b \to c$ charged current interactions. The measured value of ratio of branching ratios $R_π^l$ of $B^- \to τ^-\,ν_τ$ to $B^0 \to π^+\,ł^-\,ν$ decays, where $l = (e,\,μ)$, is larger than the standard model prediction by more than a factor of two. Similarly, a combined excess of $3.9σ$ from the standard model expectation has been reported by HFAG for the values of $R_D$ and $R_{D^{\ast}}$, where $R_{D,\,D^{\ast}}$ represents the ratio of branching ratios of $B \to (D,\,D^{\ast})\,τν$ to corresponding $B \to (D,\,D^{\ast})\,lν$ decays, respectively. Very recently, hint of lepton flavor violation has been observed in the ratio of branching fractions of $B \to K\,e^+\,e^-$ to $B \to K\,μ^+\,μ^-$ decays as well. In this context, we employ an effective Lagrangian approach to study the decay branching fractions and the ratio of branching fractions of $Λ_b \to Λ_c\,l\,ν$ and $Λ_b \to p\,l\,ν$ decays within the standard model and beyond. We constrain the new physics parameter space using the existing experimental data on $R_D$, $R_{D^{\ast}}$, and $R_π^l$. We give predictions for various observables in the context of various new physics scenarios.

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