Constraint on the branching ratio of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow></mml:msubsup><mml:mo stretchy="false">→</mml:mo><mml:mi>τ</mml:mi><mml:mover accent="true"><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math> from LEP1 data and consequences for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>R</mml:mi><mml:mo mathvariant="bold" stretchy="false">(</mml:mo><mml:msup><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mo mathvariant="bold" stretchy="false">(</mml:mo><mml:mo>*</mml:mo><mml:mo mathvariant="bold" stretchy="false">)</mml:mo></mml:mrow></mml:msup><mml:mo mathvariant="bold" stretchy="false">)</mml:mo></mml:mrow></mml:math> anomaly

Summary

Recently there has been interest in the correlation between $R({D}^{*})$ and the branching ratio (BR) of ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\tau}\overline{\ensuremath{\nu}}$ in models with a charged scalar ${H}^{\ifmmode\pm\else\textpm\fi{}}$. Any enhancement of $R({D}^{*})$ by ${H}^{\ifmmode\pm\else\textpm\fi{}}$ alone (in order to agree with current data) also enhances $\mathrm{BR}({B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\tau}\overline{\ensuremath{\nu}})$, for which there has been no direct search at hadron colliders. We show that LEP data taken at the $Z$ peak requires $\mathrm{BR}({B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\tau}\overline{\ensuremath{\nu}})\ensuremath{\lesssim}10%$, and this constraint is significantly stron