Large 2HDM(II) one-loop corrections in leptonic tau decays

The one-loop contributions to the branching ratios for leptonic τ decays are calculated in the CP-conserving 2HDM(II). The analysis is focused on large tan β enhanced contributions. We found that these contributions, involving loops with both neutral and charged Higgs bosons, dominate over the tree-level H± exchange, the latter one being totally negligible for the decay into e. We derive a simple analytical expression for the one-loop contribution which holds in the large tan β case. We show that the leptonic branching ratios of τ are complementary to the Higgsstrahlung processes for h(H) and have a large potential in constraining the parameters of the model. In this work we provide upper limits on the Yukawa couplings for both light h and light A scenarios, and we derive a new lower limit on the mass of H± as a function of tan β which differs significantly from what was considered as a standard constraint based on the tree-level H± exchange only. Interestingly we also obtain an upper limit on MH±. (orig.)