Alleviating the B̄ → Dτντ and B̄ → D∗τντ puzzle in the MSSM

We show that Supersymmetric effects driven by penguin contributions to the [Formula: see text] transition are able to account simultaneously for a sizeable increase of both branching ratios of [Formula: see text] and [Formula: see text] with respect to the Standard Model predictions, thereby approaching their experimentally measured values. We emphasize that a light chargino and neutralino, with masses less than 300 GeV, in addition to a large stau/sneutrino mass and a large [Formula: see text], are essential for enhancing the effect of the lepton penguin [Formula: see text], which is responsible for the improved theoretical predictions with respect to current data.

OBSERVABLES IN LOW-ENERGY SUPERSTRING MODELS

We compile phenomenological constraints on the minimal low-energy effective theory which can be obtained from the superstring by Calabi-Yau compactification. Mixing with the single additional neutral gauge boson in this model reduces the mass of the conventional Z0, Field vacuum expectation values are constrained by the experimental upper bound on this shift. Then, requiring the sneutrino mass squared to be positive constrains the scale of supersymmetry breaking more than do lower bounds on the masses of new charged particles and of sparticles. More model-dependent constraints follow from the “naturalness” requirement that observables do not depend sensitively on input parameters. We find a preference for the second neutral gauge boson to weigh ≲320 GeV, [Formula: see text] GeV and [Formula: see text] GeV. Dynamical generation of the gauge hierarchy is possible if mt≲70 GeV, with lower values of mt being favoured.