Probing Lepton Flavour Universality with $\Lambda_b$ decays to $\tau^+\tau^-$ final states
We present a study of the rare baryonic decay $\Lambda_b \to \Lambda \tau^+ \tau^-$ as a probe of new physics (NP) coupled preferentially to third-generation fermions. Within the Standard Model, we evaluate the branching ratio and the lepton-flavour-universality (LFU) ratio $R_{\Lambda}^{\tau/\mu}$, including both perturbative and long-distance charm contributions. We show that the LFU ratio can be predicted with an uncertainty below 10%. Possible NP effects arising from lepton non-universal dynamics are analysed within an effective field theory framework motivated by the current anomalies in $b \to c\tau\nu$ and $b \to s\mu^+\mu^-$ transitions. In this context, $R_{\Lambda}^{\tau/\mu}$ can be enhanced by several orders of magnitude, offering a clear target for upcoming searches. The implications for the related mode $\Lambda_b \to pK\tau^+\tau^-$ are also briefly discussed.