2,086 research outputs found
New physics facing LFU and LFV tests in B physics
Lepton flavor universality in the Standard Model and hints of its violation
in neutral () and charged currents in decays are
presented. We discuss model independent features as well as several leptoquark
scenarios which are well suited to fit current values of and/or
.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 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
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