550 research outputs found
Exclusive processes in factorization
The exclusive processes , in the region of which the final
state meson momentum is much larger than the hadronic scale ,
are studied in the framework of PQCD approach based on the factorization.
Including the transverse momentum distribution in the light cone wave
functions, our results are consistent with the experimental measurements.
According to our results, many processes have large enough cross sections to be
detected at GeV. The dependence of the cross section has
been directly studied and our result indicates that the scaling is more
favored than . We also find that the gluonic contribution for the
processes involving is tiny.Comment: 17 pages, including 5 figures, Revtex
The polarizability of the pion: no conflict between dispersion theory and chiral perturbation theory
Recent attempts to determine the pion polarizability by dispersion relations
yield values that disagree with the predictions of chiral perturbation theory.
These dispersion relations are based on specific forms for the absorptive part
of the Compton amplitudes. The analytic properties of these forms are examined,
and the strong enhancement of intermediate-meson contributions is shown to be
connected with spurious singularities. If the basic requirements of dispersion
relations are taken into account, the results of dispersion theory and
effective field theory are not inconsistent.Comment: 30 pages, 8 figures, 6 table
Weak productions of new charmonium in semi-leptonic decays of B_c
We study the weak productions of novel heavy mesons, such as
, , , , X(3940),
Y(3940), X(3872), and Y(4260), in the semi-leptonic decays. Since there
is still no definite answer for the components of X(3940), Y(3940), X(3872),
Y(4260) so far, we will assign them as excited charmonium states with the
possible quantum numbers constrained by the current experiments. As for the
weak transition form factors, we calculate them in the framework of light-cone
QCD sum rules approach, which is proved to be a powerful tool to deal with the
non-perturbative hadronic matrix element. Our results indicate that different
interpretations of X(3940) can result in remarkable discrepancy of the
production rate in the decays, which would help to clarify the inner
structure of the X(3940) with the forthcoming LHC-b experiments. Besides, the
predicted large weak production rates of X(3872) and Y(3940) in decays
and the small semi-leptonic decay rate for all depend on
their quantum number assignments. Moreover, the mixing of
various vector charmonium states in the weak decay of is also discussed
in this work. The future experimental measurements of these decays will test
the inner structures of these particles, according to our predictions here.Comment: 26 pages, with 7 figures, revTex
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
Evaluating decay Rates and Asymmetries of into Light Baryons in LFQM
In this work we calculate the branching ratios of semi-leptonic and
non-leptonic decays of into light baryons ( and ), as
well as the measurable asymmetries which appear in the processes, in the light
front quark model (LFQM). In the calculation, we adopt the diquark picture and
discuss the justifiability of applying the picture in our case. Our result on
the branching ratio of is in good agreement with
data. More predictions are made in the same model and the results will be
tested in the future experiments which will be conducted at LHCb and even ILC.Comment: 20 page, 8 talbes, 1 figure; Some changes were made. Accepted by PR
Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays
According to the heavy-quark flavour symmetry, the transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays and , we perform a
phenomenological study of transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate transition form factors from
to . It is found that, although being consistent with
each other within error bars, the central values of our results for form factors at , , are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table
Perturbative QCD of hard and soft processes
We discuss some problems concerning the application of perturbative QCD to
high energy processes. In particular for hard processes, we analyze higher
order and higher twist corrections. It is argued that these effects are of
great importance for understanding the behaviour of pion electromagnetic form
factor at moderately large momentum transfers. For soft processes, we show that
summing the contributions of the lowest twist operators leads to a Regge-like
amplitude.Comment: Reproduction of unpublished JINR Report E2-80-521, Dubna 1980. 22
pages 9 figures. To be published in Modern Physics Letters A. Style file is
include
Trying to understand confinement in the Schroedinger picture
We study the gauge-invariant gaussian ansatz for the vacuum wave functional
and show that it potentially possesses many desirable features of the
Yang--Mills theory, like asymptotic freedom, mass generation through the
transmutation of dimensions and a linear potential between static quarks. We
point out that these (and other) features can be studied in a systematic way by
combining perturbative and 1/n expansions. Contrary to the euclidean approach,
confinement can be easily formulated and easily built in, if not derived, in
the variational Schroedinger approach.Comment: 21 pages, 1 figure. Lecture given at the 4th St.Petersburg Winter
School in Theoretical Physics, Feb. 22-28, 199
pi/K -> e nu branching ratios to O(e^2 p^4) in Chiral Perturbation Theory
We calculate the ratios R_{e/mu}^{(P)} = Gamma(P -> e nu)/Gamma (P -> mu nu)
(P=pi,K) in Chiral Perturbation Theory to order e^2 p^4. We complement the one-
and two-loop effective theory results with a matching calculation of the local
counterterm, performed within the large- expansion. We find
R_{e/mu}^{(\pi)} = (1.2352 \pm 0.0001)*10^{-4} and R_{e/mu}^{(K)} = (2.477 \pm
0.001)*10^{-5}, with uncertainty induced by the matching procedure and chiral
power counting. Given the sensitivity of upcoming new measurements, our results
provide a clean baseline to detect or constrain effects from weak-scale new
physics in these rare decays. As a by-product, we also update the theoretical
analysis of the individual pi/K -> \ell nu modes.Comment: 40 pages, 4 figures, 3 table
The omega rho pi coupling in the VMD model revisited
We determine the value of the \omega -\rho- \pi mesons coupling
(g_{\omega\rho\pi}), in the context of the vector meson dominance model, from
radiative decays, the \omega \rightarrow 3\pi decay width and the e^+e^-
\rightarrow 3\pi cross section. For the last two observables we consider the
effect of either a heavier resonance (\rho'(1450)) or a contact term. A
weighted average of the results from the set of observables yields
g_{\omega\rho\pi} =14.7 \pm 0.1 GeV^{-1} in absence of those contributions, and
g_{\omega\rho\pi} =11.9 \pm 0.2 GeV^{-1} or g_{\omega\rho\pi} =11.7 \pm 0.1
GeV^{-1} when including the \rho' or contact term respectively. The inclusion
of these additional terms makes the estimates from the different observables to
lay in a more reduced range. Improved measurements of these observables and the
\rho'(1450) meson parameters are needed to give a definite answer on the
pertinence of the inclusion of this last one in the considered processes.Comment: 14 pages, 5 figures. Extended analysis including SND and CMD2 data.
References added. Matches published versio
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