Anatomy of $b \to c \, \tau \, \nu$ anomalies

Understand

In recent times, one of the strongest hints of Physics Beyond the Standard Model (BSM) has been the anomaly in the ratios $R_D$ and $R_{D^\ast}$ measured in the charged current decays of $B$-mesons.

• In this work, we perform a comprehensive analysis of these decay modes, first in a model independent way and subsequently, in the context of composite Higgs models.
• We discuss in depth as to how linearly realised $\rm SU(2)_L \times U(1)_Y$ symmetry imposes severe constraint on the various scenarios because of correlations with other $\Delta F =1$ processes and $Z\,\tau\,\tau$ and $Z\,\nu\,\nu$ couplings.
• In the composite Higgs paradigm with partial compositeness, we show that, irrespective of the flavour structure of the composite sector, constraints from $\Delta F =2$ processes bring the compositeness scale down to $\sim 650$ GeV which is in tension with electroweak precision observables.