Recent experimental results for the ratio of the branching fractions of Bˉ→D(∗)τνˉτ and Bˉ→D(∗)μνˉμ decays
came as a surprise and lead to a discussion of possibility to constraining New
Physics through these modes. Here we focus on B(Bˉ→Dτνˉτ)/B(Bˉ→Dμνˉμ) and argue that the result is
consistent with the Standard Model within 2σ, 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.Comment: 10 pages (published version