Constraint on the branching ratio of Bc- → τ(ν)over-bar from LEP1 data and consequences for R(D(*)) anomaly

Recently there has been interest in the correlation between R(D*) and the branching ratio (BR) of B-c(-) -> tau(nu) over bar in models with a charged scalar H-+/-. Any enhancement of R(D*) by H-+/- alone (in order to agree with current data) also enhances BR(B-c(-) -> tau(nu) over bar), for which there has been no direct search at hadron colliders. We show that LEP data taken at the Z peak requires BR(B-c(-) -> tau(nu) over bar) less than or similar to 10%, and this constraint is significantly stronger than the recent constraint BR(B-c(-) -> tau(nu) over bar) less than or similar to 30% from considering the lifetime of B-c. In order to respect this new constraint, any explanation of the R(D) and R(D*) anomaly in terms of H-+/- alone would require the future measurements of R(D*) to be even closer to the Standard Model prediction. A stronger limit on BR(B-c(-) -> tau(nu) over bar) (or its first measurement) would be obtained if the L3 Collaboration used all its data taken at the Z peak.