46 research outputs found
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
Beyond the Standard Model, guided by Lepton Universality
We discuss the current status of lepton flavour universality observables in
semileptonic charged and neutral current meson decays. We recapitulate the
current experimental situation. Assuming the current tensions with the SM are
of beyond the Standard Model origin we present their implications for the
effective theory couplings. Then we discuss general leptoquark models before
finally focussing on the model with two scalar leptoquarks ( and )
which have couplings connected by the underlying Grand Unified Theory
framework. We present the viability of the model with regard to lepton flavour
universality and present opportunities to search for this model in future
high-intensity and high-energy experimentsComment: 12 pages, 3 figures Presented at 18th International Conference on
B-Physics at Frontier Machines - Beauty201
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
Updated constraints on new physics in rare charm decays
Motivated by recent experimental results on charm physics we investigate
implications of the updated constraints of new physics in rare charm meson
decays. We first reconsider effects of the MSSM in constrained
by the recent experimental evidence on and find, that due to the
dominance of long distance physics, decay rates cannot be
modified by MSSM contributions. Then we consider effects of the extra heavy up
vector-like quark models on the decay spectrum of and
decays. We find a possibility for the tiny increase of
the differential decay rate in the region of large dilepton mass. The R-parity
violating supersymmetric model can also modify short distance dynamics in decays. We constrain relevant parameters using current upper
bound on the decay rate and investigate impact of that
constraint on the differential decay dilepton
distribution. Present bounds still allow small modification of the standard
model differential decay rate distribution.Comment: 15 pages, 4 figure
Complementarity of the constraints on New Physics from B_s -> mu+ mu- and from B -> K l+l- decays
We discuss the advantages of combining the experimental bound on Br(B_s ->
mu+ mu-) and the measured Br(B -> K l+l-) to get the model independent
constraints on physics beyond the Standard Model. Since the two decays give
complementary information, one can study not only the absolute values of the
Wilson coefficients that are zero in the Standard Model, but also their phases.
To identify the sector in which the new physics might appear, information about
the shapes of the transverse asymmetries in B -> K* l+l- at low q^2's can be
particularly useful. We also emphasize the importance of measuring the
forward-backward asymmetry in B -> K l+l- decay at large q^2's.Comment: 28 pp, 12 figures, 2 tables; v3: version as publishe
Correlating New Physics Effects in Semileptonic and Processes
We present constraints on the left-handed dimension-6 interactions that
contribute to semileptonic and leptonic decays of , , pions and to
nuclear beta decay. We employ the flavour covariant description of the
effective couplings, identify universal CP phases of New Physics and derive
constraints from decay rates and CP-odd quantities. As a result, we can predict
the maximal effects of such flavoured NP in decays from stringent decay
constraints and vice-versa.Comment: 18 pages, 10 figure