Testing the Standard Model in $B \to D τ\bar ν$ decay with minimal theory input

Recent experimental results for the ratio of the branching fractions of $\bar B \to D^{(*)}τν_τ$ and $B\to D^{(*)} μν_μ$ decays came as a surprise and lead to a discussion of possibility to constraining new physics through these modes. Here we focus on $Br(B \to D τ\barν_τ)/Br(B \to D μ\barν_μ)$ and argue that the result is consistent with the Standard Model within $2\,σ$ and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the new physics couplings.

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