1,237 research outputs found
On the four-zero texture of quark mass matrices and its stability
We carry out a new study of quark mass matrices (up-type) and
(down-type) which are Hermitian and have four zero entries, and
find a new part of the parameter space which was missed in the previous works.
We identify two more specific four-zero patterns of and
with fewer free parameters, and present two toy flavor-symmetry
models which can help realize such special and interesting quark flavor
structures. We also show that the texture zeros of and
are essentially stable against the evolution of energy scales in
an analytical way by using the one-loop renormalization-group equations.Comment: 33 pages, 4 figures, minor comments added, version to appear in Nucl.
Phys.
The effective neutrino mass of neutrinoless double-beta decays: how possible to fall into a well
If massive neutrinos are the Majorana particles and have a normal mass
ordering, the effective mass term of a neutrinoless
double-beta () decay may suffer significant cancellations among
its three components and thus sink into a decline, resulting in a "well" in the
three-dimensional graph of against the smallest
neutrino mass and the relevant Majorana phase . We present a new
and complete analytical understanding of the fine issues inside such a well,
and discover a novel threshold of in terms of the
neutrino masses and flavor mixing angles: in connection with and . This threshold point, which links the
{\it local} minimum and maximum of , can be used to
signify observability or sensitivity of the future -decay
experiments. Given current neutrino oscillation data, the possibility of
is found to be
very small.Comment: 9 pages, 3 figures, version to appear in Eur. Phys. J.
Weak decays of doubly heavy baryons: the case
As a continuation of our previous works, we investigate the weak decays of
doubly heavy baryons into a spin- singly or doubly heavy baryon.
Light-front approach is adopted to handle the dynamics in the transitions, in
which the two spectator quarks are approximated as a diquark. Results for form
factors are then used to calculate decay widths of semi-leptonic and
nonleptonic processes. The flavor SU(3) symmetry and symmetry breaking effects
in semi-leptonic decays modes are explored, and we point out that in charm
sector, there are sizable symmetry breaking effects. For nonleptonic decay
modes, we study only the factorizable channels induced by the external
W-emission. We find that branching fractions for most 1/2 to 3/2 transitions
are approximately one order of magnitude smaller than the corresponding ones
for the 1/2 to 1/2 transitions. Parametric uncertainties are also investigated
in detail. This work, together with our previous works, are beneficial to the
experimental studies of doubly heavy baryons at LHC and other experiments.Comment: 23 pages, 2 figure
Revisiting the four-quark operator matrix elements for the lifetime of
Heavy quark expansion can nicely explain the lifetime of .
However, there still exsit sizable uncertainties from the four-quark operator
matrix elements in the power of . In this work, the leading order
results of the four-quark operator matrix elements
and
are
obtained using full QCD sum rules. Contributions from dimension-0,3,5 are
considered. It turns out that the contributions from dimension-3,5 are
proportional to the mass of quark. Stable Borel region can be found, and
for this reason, the uncertainties caused by the QCD sum rule parameters are
small. The leading logarithmic corrections are also considered, which turn out
to be a little destructive. Our results are close to the lower bound of the
existing theoretical predictions.Comment: 9 pages, 2 figure
Weak Decays of Doubly Heavy Baryons: the case
Very recently, the LHCb collaboration has observed in the final state
a resonant structure that is identified as the
doubly-charmed baryon . Inspired by this observation, we
investigate the weak decays of doubly heavy baryons ,
, , ,
, , ,
and and focus on the decays into spin
baryons in this paper. At the quark level these decay processes are induced by
the or transitions, and the two spectator quarks can be
viewed as a scalar or axial vector diquark. We first derive the hadronic form
factors for these transitions in the light-front approach and then apply them
to predict the partial widths for the semi-leptonic and non-leptonic decays of
doubly heavy baryons. We find that a number of decay channels are sizable and
can be examined in future measurements at experimental facilities like LHC,
Belle II and CEPC.Comment: 40 pages, 4 figures, to appear in EPJ
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