242,167 research outputs found
The self-penguin contribution to
We consider the contribution to decays from the
non-diagonal s \ra d quark transition amplitude. First, we calculate the most
important part of the transition, the so-called self-penguin
amplitude , including the heavy top-quark case. Second, we
calculate the matrix element of the transition for the
physical process. This part of the analysis is performed
within the Chiral Quark Model where quarks are coupled to the pseudoscalar
mesons. The CP-conserving self-penguin contribution to is
found to be negligible. The obtained contribution to is
sensitive to the values of the quark condensate and the
constituent quark mass . For reasonable values of these quantities we find
that the self-penguin contribution to is 10-15% of the
gluonic penguin contribution and has the same sign. Given the large
cancellation between gluonic and electroweak penguin contributions, this means
that our contribution is of the same order of magnitude as
itself.Comment: Latex, 12 pages, 2 figure
Non-leptonic decays in an extended chiral quark model
We consider the color suppressed (nonfactorizable) amplitude for the decay
mode . We treat the -quark in the
heavy quark limit and the energetic light () quarks within a variant of
Large Energy Effective Theory combined with an extension of chiral quark
models. Our calculated amplitude for
is suppressed by a factor of order with respect to the
factorized amplitude, as it should according to QCD-factorization. Further, for
reasonable values of the (model dependent) gluon condensate and the constituent
quark mass, the calculated nonfactorizable amplitude for can easily accomodate the experimental value.
Unfortunately, the color suppressed amplitude is very sensitive to the values
of these model dependent parameters. Therefore fine-tuning is necessary in
order to obtain an amplitude compatible with the experimental result for
.Comment: 10 pages, 6 figures. Presented at QCD@work, Lecce, Italy, june 201
Color suppressed contributions to the decay modes B_{d,s} -> D_{s,d} D_{s,d}, B_{d,s} -> D_{s,d} D^*_{s,d}, and B_{d,s} -> D^*_{s,d} D^*_{s,d}
The amplitudes for decays of the type , have no
factorizable contributions, while , and have relatively small factorizable contributions
through the annihilation mechanism. The dominant contributions to the decay
amplitudes arise from chiral loop contributions and tree level amplitudes which
can be obtained in terms of soft gluon emissions forming a gluon condensate. We
predict that the branching ratios for the processes ,
and are all
of order , while ,
and are of
order . We obtain branching ratios for two 's in
the final state of order two times bigger.Comment: 15 pages, 4 figure
Chiral quark models and their applications
We give an overview of chiral quark models, both for the pure light sector
and the heavy-light sector.
We describe how such models can be bosonized to obtain welWe give an overview
of chiral quark models, both for the pure light sector and the heavy-light
sector.
We describe how such models can be bosonized to obtain well known chiral
Lagrangians which can be inferred from the symmetries of QCD alone. In
addition, we can within these models calculate the coefficients of the various
pieces of the chiral Lagrangians. We discuss a few applications of the models,
in particular, \bbar mixing and processes of the type ,
where might be both pseudoscalar and vector. We suggest how the formalism
might be extended to include light vectors (), and heavy to
light transitions like . l known chiral Lagrangians which can be
inferred from the symmetries of QCD alone. In addition, we can within these
models calculate the coefficients of the various pieces of the chiral
Lagrangians. We discuss a few applications of the models, in particular,
\bbar mixing and processes of the type , where might be
both pseudoscalar and vector. We suggest how the formalism might be extended to
include light vectors (), and heavy to light transitions like
.Comment: 37 pages, 16 figures. Dedicated to the memory of Prof. D. Tadic,
Submitted to Fizika B, Zagre
Non-factorizable effects in B-anti-B mixing
We study the B-parameter (``bag factor'') for B-anti-B mixing within a
recently developed heavy-light chiral quark model. Non-factorizable
contributions in terms of gluon condensates and chiral corrections are
calculated. In addition, we also consider 1/m_Q corrections within heavy quark
effective field theory. Perturbative QCD effects below \mu = m_b known from
other work are also included. Considering two sets of input parameters, we find
that the renormalization invariant B-parameter is B = 1.51 +- 0.09 for B_d and
B = 1.40 +- 0.16 for B_s.Comment: 23 pages, 7 figures, RevTex 4 Small changes, included more details in
the tex
The Isgur-Wise Function within a Modified Heavy-Light Chiral Quark Model
We consider the Isgur-Wise function xi(omega) within a new modified version
of a heavy-light chiral quark model. While early versions of such models gave
too small absolute value of the slope, namely xi'(1) of about -0.4 to -0.3, we
show how extended version(s) may lead to values around -1, in better agreement
with recent measurements. This is obtained by introducing a new mass parameter
in the heavy quark propagator. We also shortly comment on the consequences for
the decay modes B --> D D-bar.Comment: 20 pages, 7 PS figure, LaTe
The \beta-term for D^* --> D \gamma within a heavy-light chiral quark model
We present a calculation of the \beta-term for D^* --> D gamma within a
heavy-light chiral quark model. Within the model, soft gluon effects in terms
of the gluon condensate with lowest dimension are included. Also, calculations
of 1/m_c corrections are performed. We find that the value of \beta is rather
sensitive to the constituent quark mass compared to other quantities calculated
within the same model. Also, to obtain a value close to the experimental value,
one has to choose a constituent light quark mass larger than for other
quantities studied in previous papers. For a light quark mass in the range 250
to 300 MeV and a quark condensate in the range -(250-270 MeV)^3 we find the
value (2.5 +- 0.6) GeV^-1. This value is in agreement with the value of \beta
extracted from experiment 2.7 +- 0.2 GeV^-1.Comment: 16 pages, 5 figure
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