B physics offers important tests of the Standard Model at low energies. Recently, BaBar observed significant deviations from the Standard Model expectations in the semileptonicB→D(∗)τmathτ decays. Interestingly, the measured leptonic B→τν branching fraction also deviates from CKM unitarity predictions. Motivated by these results we investigate the most general set of lowest dimensional effective operators leading to modifications ofb→c(u) (semi)tauonic transitions. Allowing for general flavor violation, we find that among possible operator structures, new contributions from right-right vector and right-left scalar quark currents provide viable explanations of the anomalies. In addition, we identify a number of B→D∗τmathτ transition observables with the power to discriminate among the various effective operators' contributions. They are the differential decay rate, longitudinalD∗ polarization fraction, D∗-τ opening angle asymmetry and the τ helicity asymmetry.

COBISS.SI-ID: 25811495

The BaBar experiment has recently measured anomalously large decay widths of B -) D tau nu and B → D∗τν ̄ . Being a tree-level processes in the SM one does not expect visible contributions of beyond the Standard model physics in these processes therefore the revision the Standard model predictions of these decays is urgent. We have focused on the decay channel with pseudoscalar D in the final state due to firmer theoretical grip as one needs only two hadronic form factors. We have put forward a new method of predicting decay widths, where the need to use nonperturbative input, which is always the main source of error, is limited to very narrow kinematical region. In the larger portion of the phase space one can rely instead on the measured spectra in B -) D ell nu decays, where ell is a light lepton. The chi-squared combined analysis of the two decay modes with light and tau leptons reveals that the disagreement of the B -) D tau nu with the SM prediction is less than 2 sigma. We have observed that the discrepancy can be removed completely in models with scalar on tensor effective operators.

COBISS.SI-ID: 26057511

We explored the implications of the recent experimental evidence for charm CP violation both within the standard model (SM) and beyond. In the absence of reliable methods to evaluate the hadronic matrix elements involved, we estimated qualitatively the magnitude of the non-SM contributions required to generate the observed central value. In the context of an effective theory, we listed the operators that can give rise to the measured CP violation and investigated constraints on them from other processes.

COBISS.SI-ID: 25741863