534 research outputs found
Double charmonium production in exclusive bottomonia decays
This paper is devoted to the leading twist exclusive bottomonia decays with
double charmonium in the final state. Using models of the twist-2 charmonia
distribution amplitudes the widths of these decays are calculated within light
cone formalism. In addition, the processes under consideration are studied
within nonrelativistic QCD. In our analysis we have found that the production
of some of the -wave charmonia mesons with is allowed already
at the leading twist approximation. This means that the selection rules which
predict the suppression of such decays are violated. The mechanism which lies
behind this violation is discussed.Comment: Minor changes, some references adde
Study of exclusive processes e^+ e^- \to VP
This paper is devoted to consideration of the hard exclusive processes
, where . Experimental measurement of
the cross section of the process at BaBar collaboration
at large center mass energy GeV and some low energy experimental
data GeV give us the possibility to study the cross section
in the broad energy region. As the result, we have determined the asymptotic
behavior of the cross section of in the limit , which is in agreement with perturbative QCD prediction. Assuming that
the same asymptotic behavior is valid for the other processes under
consideration and using low energy experimental data we have predicted the
cross sections of these processes at energies GeV. In
addition, we have calculated the cross sections of these processes at the same
energies within perturbative QCD. Our results are in agreement with available
experimental data.Comment: 10 pages, 2 tables, 6 figures; minor changes; article accepted to
publication is Phys. Rev.
Mass Spectrum in SQCD and Problems with the Seiberg Duality. Another Scenario
N=1 SQCD with SU(N_c) colors and N_F flavors of light quarks is considered
within the dynamical scenario which assumes that quarks can be in two different
phases only. These are: a) either the HQ (heavy quark) phase where they are
confined, b) or they are higgsed, at the appropriate values of parameters of
the Lagrangian.
The mass spectra of this (direct) theory and its Seiberg's dual are obtained
and compared, for quarks of equal or unequal masses. It is shown that in all
cases when there is the additional small parameter at hand (it is
0<(3N_c-N_F)/N_F << 1 for the direct theory, or its analog 0<(2N_F-3N_c)/N_F <<
1 for the dual one), the mass spectra of the direct and dual theories are
parametrically different. A number of other regimes are also considered.Comment: 30 pages, purely technical improvements for readers convenienc
Nucleon Form Factors to Next-to-Leading Order with Light-Cone Sum Rules
We have calculated the leading-twist next-to-leading order (NLO), i.e.,
O(alpha_s), correction to the light-cone sum-rules prediction for the
electromagnetic form factors of the nucleon. We have used the Ioffe nucleon
interpolation current and worked in M_N=0 approximation, with M_N being the
mass of the nucleon. In this approximation, only the Pauli form factor F_2
receives a correction and the calculated correction is quite sizable (cca 60%).
The numerical results for the proton form factors show the improved agreement
with the experimental data. We also discuss the problems encountered when going
away from M_N=0 approximation at NLO, as well as, gauge invariance of the
perturbative results. This work presents the first step towards the NLO
accuracy in the light-cone sum rules for baryon form factors.Comment: 68 pages, 9 figures; minor typos in the text corrected in accordance
with the published versio
A consistent model for \pi N transition distribution amplitudes and backward pion electroproduction
The extension of the concept of generalized parton distributions leads to the
introduction of baryon to meson transition distribution amplitudes (TDAs),
non-diagonal matrix elements of the nonlocal three quark operator between a
nucleon and a meson state. We present a general framework for modelling nucleon
to pion () TDAs. Our main tool is the spectral representation for \pi N
TDAs in terms of quadruple distributions. We propose a factorized Ansatz for
quadruple distributions with input from the soft-pion theorem for \pi N TDAs.
The spectral representation is complemented with a D-term like contribution
from the nucleon exchange in the cross channel. We then study backward pion
electroproduction in the QCD collinear factorization approach in which the
non-perturbative part of the amplitude involves \pi N TDAs. Within our two
component model for \pi N TDAs we update previous leading-twist estimates of
the unpolarized cross section. Finally, we compute the transverse target single
spin asymmetry as a function of skewness. We find it to be sizable in the
valence region and sensitive to the phenomenological input of our \pi N TDA
model.Comment: 39 pages, 9 figure
Excited charmonium mesons production in e^+e^- annihilation at \sqrt{s}=10.6 GeV
In this paper the production of excited vector and pseudoscalar charmonium
mesons in \epem annihilation is analyzed in the framework of light cone. In
particular the cross sections \epem \to \psi(2S)\eta_c(1S),
\psi(1S)\eta_c(2S),\psi(2S)\eta_c(2S) have been calculated. It is shown, that
contrary to NRQCD the cross sections calculated in the framework of light cone
agree with experimental data.Comment: 7 pages; 2 figures, some refrences adde
A three-loop check of the 'a - maximization' in SQCD with adjoint(s)
The 'a - maximization' was introduced by K. Inrtiligator and B. Wecht for
finding anomalous dimensions of chiral superfields at the IR fixed points of
the RG flow. Using known explicit calculations of anomalous dimensions in the
perturbation theory of SQCD (with one or two additional adjoint fields), it is
checked here at the three-loop level.Comment: 5 pages; the title changed, the text improved and expande
Statistics of Entropy Production in Linearized Stochastic System
We consider a wide class of linear stochastic problems driven off the
equilibrium by a multiplicative asymmetric force. The force brakes detailed
balance, maintained otherwise, thus producing entropy. The large deviation
function of the entropy production in the system is calculated explicitly. The
general result is illustrated using an example of a polymer immersed in a
gradient flow and subject to thermal fluctuations.Comment: 4 pages, 1 figur
The Proton Electromagnetic Form Factor and Quark Orbital Angular Momentum
We analyze the proton electromagnetic form factor ratio
as a function of momentum transfer
within perturbative QCD. We find that the prediction for at large
momentum transfer depends on the exclusive quark wave functions, which are
unknown. For a wide range of wave functions we find that $ QF_2/F_1 \sim\
const$ at large momentum transfer, in agreement with recent JLAB data.Comment: 8 pages, 2 figures. To appear in Proceedings of the Workshop QCD
2002, IIT Kanpur, 18-22 November (2002
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