New physics facing LFU and LFV tests in B physics

Lepton flavor universality in the Standard Model and hints of its violation in neutral ($R_K$) and charged currents $(R_{D^{(*)}})$ in $B$ decays are presented. We discuss model independent features as well as several leptoquark scenarios which are well suited to fit current values of $R_K$ and/or $R_{D^{(*)}}$.Comment: 9 pages, 2 figures, Proceedings for the LHCP Conference, Lund, June 201

Model independent constraints on leptoquarks from b -> s l+ l- processes

We list all scalar and vector leptoquark states that contribute to the b -> s l+ l- effective Hamiltonian. There are altogether three scalar and four vector leptoquarks that are relevant. For contribution of each state we infer the correlations between effective operators and find that only two baryon number-violating vector leptoquarks give rise to scalar and pseudoscalar four-fermion operators, whereas the scalar states can contribute to those operators only when two states with same charge are present. We bound the resulting Wilson coefficients by imposing experimental constraints coming from branching fractions of B -> K l+ l-, B_s -> mu+ mu-, and B -> X_s mu+ mu- decays.Comment: 10 pages, 3 figures, 1 table; v2: minor corrections, added reference

Heavy and light scalar leptoquarks in proton decay

We list scalar leptoquarks that mediate proton decay via renormalizable couplings to the Standard Model fermions. We employ a general basis of baryon number violating operators to parameterize contributions of each leptoquark towards proton decay. This then sets the stage for investigation of bounds on the leptoquark couplings to fermions with respect to the most current Super Kamiokande results on proton stability. We quantify if, and when, it is necessary to have leptoquark masses close to a scale of grand unification in the realistic SU(5) and flipped SU(5) frameworks. The most and the least conservative lower bounds on the leptoquark masses are then presented. We furthermore single out a leptoquark without phenomenologically dangerous tree-level exchanges that might explain discrepancy of the forward-backward asymmetries in $t \bar t$ production observed at Tevatron, if relatively light. The same state could also play significant role in explaining muon anomalous magnetic moment. We identify contributions of this leptoquark to dimension-six operators, mediated through a box diagram, and tree-level dimension-nine operators, that would destabilize proton if sizable leptoquark and diquark couplings were to be simultaneously present.Comment: 26 pp, 2 figures, extensive expansion of Section V with new result

Leptoquarks in FCNC charm decays

Recently it was noticed that among many scenarios of new physics leptoquarks might compensate for the disagreement between the lattice and experimental results for the charmed strange meson decay constant. The leptoquarks might modify also the flavor changing neutral current charm decays. In this study we investigate impact of the scalar leptoquark with electric charge -1/3 on the dilepton invariant mass distribution in the D^+ --> pi^+ mu^+ mu^- decay and on the branching ratios of the D^0 --> mu^+ mu^- using the existing experimental results.Comment: 5 pages, 1 figur