6,853 research outputs found
decay in scalar and vector leptoquark scenarios
It has been shown that the anomalies observed in and decays can be
resolved by adding a single scalar or vector leptoquark to the Standard Model,
while constraints from other precision measurements in the flavour sector can
be satisfied without fine-tuning. To further explore these two interesting
scenarios, in this paper, we study their effects in the semi-leptonic
decay. Using the best-fit solutions for
the operator coefficients allowed by the current data of mesonic decays, we
find that (i) the two scenarios give similar amounts of enhancements to the
branching fraction and the
ratio , (ii) the
two best-fit solutions in each of these two scenarios are also
indistinguishable from each other, (iii) both scenarios give nearly the same
predictions as those of the Standard Model for the longitudinal polarizations
of and as well as the lepton-side forward-backward
asymmetry. With future measurements of these observables in
decay at the LHCb, the two leptoquark
scenarios could be further tested, and even differentiated from the other NP
explanations for the anomalies. We also discuss the
feasibility for the measurements of these observables at the LHC and the future
colliders.Comment: 29 pages, 4 tables and 2 figures; More references and the feasibility
for the measurements of the observables in these decays at the LHC and the
future colliders added, final version published in the journa
Revisiting B\to\pi K, \pi K^{\ast} and \rho K decays: CP violations and implication for New Physics
Combining the up-to-date experimental information on and decays, we revisit the decay rates and CP asymmetries of
these decays within the framework of QCD factorization. Using an infrared
finite gluon propagator of Cornwall prescription, we find that the time-like
annihilation amplitude could contribute a large strong phase, while the
space-like hard spectator scattering amplitude is real. Numerically, we find
that all the branching ratios and most of the direct CP violations, except
, agree with the current experimental data
with an effective gluon mass . Taking the unmatched
difference in direct CP violations between and
decays as a hint of new physics, we perform a
model-independent analysis of new physics contributions with a set of
(q=u,d) operators. Detail
analyses of the relative impacts of the operators are presented in five cases.
Fitting the twelve decay modes, parameter spaces are found generally with
nontrivial weak phases. Our results may indicate that both strong phase from
annihilation amplitude and new weak phase from new physics are needed to
resolve the puzzle. To further test the new physics hypothesis, the
mixing-induced CP violations in and are
discussed and good agreements with the recent experimental data are found.Comment: Version published in JHE
Freeze-in Dirac neutrinogenesis: thermal leptonic CP asymmetry
We present a freeze-in realization of the Dirac neutrinogenesis in which the
decaying particle that generates the lepton-number asymmetry is in thermal
equilibrium. As the right-handed Dirac neutrinos are produced non-thermally,
the lepton-number asymmetry is accumulated and partially converted to the
baryon-number asymmetry via the rapid sphaleron transitions. The necessary
CP-violating condition can be fulfilled by a purely thermal kinetic phase from
the wavefunction correction in the lepton-doublet sector, which has been
neglected in most leptogenesis-based setup. Furthermore, this condition
necessitates a preferred flavor basis in which both the charged-lepton and
neutrino Yukawa matrices are non-diagonal. To protect such a proper Yukawa
structure from the basis transformations in flavor space prior to the
electroweak gauge symmetry breaking, we can resort to a plethora of model
buildings aimed at deciphering the non-trivial Yukawa structures.
Interestingly, based on the well-known tri-bimaximal mixing with a minimal
correction from the charged-lepton or neutrino sector, we find that a
simultaneous explanation of the baryon-number asymmetry in the Universe and the
low-energy neutrino oscillation observables can be attributed to the mixing
angle and the CP-violating phase introduced in the minimal correction.Comment: 28 pages and 7 figures; more discussions and one figure added, final
version published in the journa
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