# Phenomenology of $\Lambda_b \to \Lambda_c \tau \bar{\nu}_{\tau}$ using lattice QCD calculations

## TL;DR

This paper uses lattice QCD to calculate form factors for the $ ext{Lambda}_b o ext{Lambda}_c$ decay, including tensor form factors, and explores how these can constrain new physics models related to the $R(D^{(*)})$ puzzle.

## Contribution

It provides the first lattice QCD calculations of tensor form factors for $ ext{Lambda}_b o ext{Lambda}_c$ decay and analyzes their implications for new physics constraints.

## Key findings

- Calculated tensor form factors using lattice QCD.
- Showed $R( ext{Lambda}_c)$ measurement constrains new physics models.
- Enhanced understanding of $ ext{Lambda}_b o ext{Lambda}_c$ decay observables.

## Abstract

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic $\Lambda_b \to \Lambda_c \tau \bar{\nu}_{\tau}$ decay. This decay is of interest in light of the $R({D^{(*)}})$ puzzle in the semileptonic $\bar{B} \to D^{(*)} \tau {\bar\nu}_\tau$ 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 $R(\Lambda_c) = {\cal B}[\Lambda_b \to \Lambda_c \tau \bar{\nu}_{\tau}] / {\cal B}[\Lambda_b \to \Lambda_c \ell \bar{\nu}_{\ell}]$ can strongly constrain the NP parameters of models discussed for the $R({D^{(*)}})$ puzzle. We use form factors from lattice QCD to calculate all $\Lambda_b \to \Lambda_c \tau \bar{\nu}_{\tau}$ observables. The $\Lambda_b \to \Lambda_c$ tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.