665 research outputs found
Study of pure annihilation type decays
In this work, we calculate the rare decays and in perturbative QCD approach with Sudakov resummation.
We give the branching ratio of for , which will
be tested soon in factories.
The decay has a very small branching ratio at
, due to the suppression from CKM matrix elements . It may be sensitive to new physics contributions.Comment: 14 pages, 1 figur
Perturbative QCD analysis of decays
We study the first observed charmless modes, the
decays, in perturbative QCD formalism. The obtained branching ratios
are larger than
from QCD factorization. The comparison of the predicted magnitudes and phases
of the different helicity amplitudes, and branching ratios with experimental
data can test the power counting rules, the evaluation of annihilation
contributions, and the mechanism of dynamical penguin enhancement in
perturbative QCD, respectively.Comment: 14 pages, 2 tables, brief disscussion on hard sacle added, version to
appear in PR
Molecular mechanisms underlying anti-tumor promoting activities of heat-processed Panax ginseng C.A. Meyer.
Recently, there have been considerable efforts to search for naturally occurring substances that can inhibit, reverse, or retard the multi-stage carcinogenesis. A wide array of phenolic substances derived from edible and medicinal plants have been reported to possess anticarcinogenic and antimutagenic activities and in many cases, the chemopreventive activities of phytochemicals are associated with their anti-inflammatory and/or antioxidative properties. Panax ginseng C.A. Meyer cultivated in Korea has been widely used in traditional herbal medicine for the treatment of various diseases. Certain fractions or purified ingredients of ginseng have been shown to exert anticarcinogenic and antimutagenic activities. Our previous studies have revealed that the methanol extract of heat-processed Panax ginseng C.A. Meyer attenuates the lipid peroxidation in rat brain homogenates and is also capable of scavenging superoxide generated by xanthine- xanthine oxidase or by 12-O-tetradecanoylphorbol-13-acetate (TPA) in differentiated human promyelocytic leukemia (HL-60) cells. Topical application of the same extract onto shaven backs of female ICR mice also suppressed TPA-induced skin tumor promotion. Likewise, topical application of ginsenoside Rg3, one of the constituents of heat-treated ginseng, significantly inhibited TPA-induced mouse epidermal ornithine decarboxylase activity and skin tumor promotion. Expression of cyclooxygenase-2 (COX-2) in TPA-stimulated mouse skin was markedly suppressed by Rg3 pretreatment. In addition, Rg3 inhibited TPA-stimulated activation of NF-kappaB and extracellular-regulated protein kinase (ERK), one of the mitogen-activated protein (MAP) kinase in mouse skin and also in cultured human breast epithelial cells (MCF-10A)
B meson light-cone wavefunctions in the heavy quark limit
We present a systematic study of the B meson light-cone wavefunctions in QCD
in the heavy-quark limit. We construct model-independent formulae for the
light-cone wavefunctions in terms of independent dynamical degrees of freedom,
which exactly satisfy the QCD equations of motion and constraints from
heavy-quark symmetry. The results demonstrate novel behaviors of longitudinal
as well as transverse momentum distribution in the B mesons.Comment: 5 pages LaTeX, 1 style file. Talk presented at RADCOR/Loops and Legs
2002, Kloster Banz, Germany, September 8-13, 200
Study of color suppressed modes
The color suppressed modes are
analyzed in perturbative QCD approach. We find that the dominant contribution
is from the non-factorizable diagrams. The branching ratios calculated in our
approach for agree with current experiments. By
neglecting the gluonic contribution, we predict the branching ratios of are at the comparable size of , but smaller than that of .Comment: revtex, 5 pages, axodraw.st
factorization of exclusive processes
We prove factorization theorem in perturbative QCD (PQCD) for exclusive
processes by considering and . The relevant form factors are expressed as the convolution of hard
amplitudes with two-parton meson wave functions in the impact parameter
space, being conjugate to the parton transverse momenta . The point is
that on-shell valence partons carry longitudinal momenta initially, and acquire
through collinear gluon exchanges. The -dependent two-parton wave
functions with an appropriate path for the Wilson links are gauge-invariant.
The hard amplitudes, defined as the difference between the parton-level
diagrams of on-shell external particles and their collinear approximation, are
also gauge-invariant. We compare the predictions for two-body nonleptonic
meson decays derived from factorization (the PQCD approach) and from
collinear factorization (the QCD factorization approach).Comment: 11 pages, REVTEX, 5 figure
Threshold resummation for exclusive B meson decays
We argue that double logarithmic corrections need to be
resumed in perturbative QCD factorization theorem for exclusive meson
decays, when the end-point region with a momentum fraction is
important. These double logarithms, being of the collinear origin, are absorbed
into a quark jet function, which is defined by a matrix element of a quark
field attached by a Wilson line. The factorization of the jet function from the
decay is proved to all orders. Threshold resummation for
the jet function leads to a universal, {\it i.e.}, process-independent, Sudakov
factor, whose qualitative behavior is analyzed and found to smear the end-point
singularities in heavy-to-light transition form factors.Comment: 10 pages, more details are include
Possible Large Direct CP Violations in Charmless B-Decays
We discuss the perturbative QCD approach for the exclusive two body B-meson
decays to light mesons. We briefly review its ingredients and some important
theoretical issues on factorization approach. We show numerical results which
are compatible with present experimantal data for the charmless B-meson decays.
Specailly we predict the possibility of large direct CP violation effects in
and .
In the last section we investigate two methods to determine the weak phases
and from processes. We obtain bounds on
and from present experimental measurements.Comment: 18 pages, latex, 8 figures and 8 tables, typos corrected and added
more tables and references. Presented at the 3rd workshop on Higher
Luminosity B Factory, 6-7 August 2002, Kanagawa, Japan; Submitted to Phys.
Rev.
QCD factorization for B -> PP
In this work, we give a detailed discussion for QCD factorization involved
the complete chirally enhanced power corrections for B decays to two light
pseudoscalar mesons, and present some detailed calculations of radiative
corrections at the order of alpha_s. We point out that the infrared finiteness
of the vertex corrections in the chirally enhanced power corrections requires
twist-3 light-cone distribution amplitudes (LCDAs) of the light pseudoscalar
symmetric. However, even in the symmetric condition, there is also logarithmic
divergence from the endpoints of the twist-3 LCDAs in the hard spectator
scattering. We point out that the decay amplitudes of B --> PP predicted by QCD
factorization are really free of the renormalization scale dependence, at least
at the order of alpha_s. At last, we briefly compare the QCD factorization with
the generalized factorization and PQCD method.Comment: 31 pages, 3 eps figure
Perturbative QCD factorization of and
We prove factorization theorem for the processes and
to leading twist in the covariant gauge by means of the
Ward identity. Soft divergences cancel and collinear divergences are grouped
into a pion wave function defined by a nonlocal matrix element. The gauge
invariance and universality of the pion wave function are confirmed. The proof
is then extended to the exclusive meson decays and
in the heavy quark limit. It is shown that a light-cone
meson wave function, though absorbing soft dynamics, can be defined in an
appropriate frame. Factorization of the decay in
space, being parton transverse momenta, is briefly discussed. We comment
on the extraction of the leading-twist pion wave function from experimental
data.Comment: 21 pages in Latex file, version to appear in Phys. Rev.
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