184 research outputs found

### Instanton-induced production of QCD jets

We consider the instanton contributions for the production of a gluon jet
with large transverse momentum in QCD. We find that Mueller's corrections
corresponding to the rescattering of hard quanta are likely to remove
contributions of large instantons, making this cross section well defined. This
observation generalizes the previous discussion of instanton effects in the
deep inelastic scattering and suggests that all hard processes in the QCD
receive hard non-perturbative corrections from instantons of small size, of
order $\rho\sim 1/(Q\alpha_s)$.Comment: LATEX, 7 pages, DESY 94-17

### Instanton-induced production of jets with large transverse momentum in QCD

We consider the instanton-induced cross section for production of a gluon jet
with large transverse momentum in QCD and point out that Mueller's corrections
corresponding to the rescattering of hard quanta are likely to remove
contributions of large instantons, making this cross section well defined. Some
speculations about possible phenomenological signatures are presented.Comment: LATEX, requires espcrc2.sty file, appended at the end. (Invited talk
presented by V. Braun at the conference ``QCD-94'', Montpellier, France, July
7 -13, 1994), MPI-PhT/94-5

### A momentum Space Analysis of the Triple Pomeron Vertex in pQCD

We study properties of the momentum space Triple Pomeron Vertex in
perturbative QCD. Particular attention is given to the collinear limit where
transverse momenta on one side of the vertex are much larger than on the other
side. We also comment on the kernels in nonlinear evolution equations.Comment: Minor misprints corrected. To be published in EPJ

### The magnetic moments of 'Lambda_b' and 'Lambda_c' baryons in light cone QCD sum rules

Using the most general form of the interpolating currents of heavy baryons,
the magnetic moments of heavy baryons "Lambda_Q (Q=b,c)" are calculated in
framework of the light cone QCD sum rules. A comparison of our results on
magnetic moments with the existing theoretical results calculated in various
other frameworks are presented.Comment: 14 pp, 6 figures (postscript formatted), LaTex formatte

### Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering

We argue that parton distributions in coordinate space provide a more natural
object for nonperturbative methods compared to the usual momentum distributions
in which the physics of different longitudinal distances is being mixed. To
illustrate the advantages of the coordinate space formulation, we calculate the
coordinate space distributions for valence quarks in the proton using the QCD
sum rule approach. A remarkable agreement is found between the calculated and
the experimentally measured u-quark distribution up to light-cone distances
$\Delta^- = \Delta^0 - \Delta^3$ of order $\sim 1$ fm in the proton rest frame.
The calculation for valence d quarks gives much worse results; the reasons for
this discrepancy are discussed.Comment: 24 pages plus 13 pages with figures, requires epsf.sty, revised
version to appear in Phys.Rev.

### Light-Ray Evolution Equations and Leading-Twist Parton Helicity-Dependent Nonforward Distributions

We discuss the calculation of the evolution kernels \Delta W_{\zeta}(X,Z) for
the leading-twist nonforward parton distributions G_\zeta(X,t) sensitive to
parton helicities. We present our results for the kernels governing evolution
of the relevant light-ray operators and describe a simple method allowing to
obtain from them the components of the nonforward kernels \Delta
W_{\zeta}(X,Z).Comment: 8 pages; final version, to appear in Physics Letters

### Non-linear QCD dynamics and exclusive production in $ep$ collisions

The exclusive processes in electron-proton ($ep$) interactions are an
important tool to investigate the QCD dynamics at high energies as they are in
general driven by the gluon content of proton which is strongly subject to
parton saturation effects. In this paper we compute the cross sections for the
exclusive vector meson production as well as the deeply virtual Compton
scattering (DVCS) relying on the color dipole approach and considering the
numerical solution of the Balitsky-Kovchegov equation including running
coupling corrections. We show that the small-$x$ evolution given by this
evolution equation is able to describe the DESY-HERA data and is relevant for
the physics of the exclusive observables in future electron-proton colliders
and in photoproduction processes to be measured in coherent interactions at the
LHC.Comment: 6 pages, 4 figure

### A solvable model for small-x physics in D > 4 dimensions

I present a simplified model for the gluon Green's function governing
high-energy QCD dynamics, in arbitrary space-time dimensions. The BFKL integral
equation (either with or without running coupling) reduces to a second order
differential equation that can be solved in terms of Bessel and hypergeometric
functions. Explicit expressions for the gluon density and its anomalous
dimension are derived in MS and Q_0 factorization schemes. This analysis
illustrates the qualitative features of the QCD gluon density in both
factorization schemes. In addition, it clarifies the mathematical properties
and validates the results of the ``gamma-representation'' method proposed by
M.Ciafaloni and myself for extracting resummed next-to-leading-log x anomalous
dimensions of phenomenological relevance in the two schemes.Comment: 30 pages, 9 figure

### The (Sigma_Q-Lambda_Q) transition magnetic moments in light cone QCD sum rules

Using the general form of (Sigma_Q) and (Lambda_Q) (Q=b or c) currents,
(Sigma_Q-Lambda_Q) transition magnetic moments are calculated in framework of
the light cone QCD sum rules method. In this approach nonperturbative effects
are described by the photon wave functions and only two-particle photon wave
functions are taken into account. Our predictions on transition magnetic
moments are (mu_{Sigma_c Lambda_c} = - (1.5 pm 0.4) mu_N) and (mu_{Sigma_b
Lambda_b} = - (1.6 pm 0.4) mu_N). A comparison of our results with the ones
existing in the literature is given.Comment: 15 pp, 6 figures (postscript formatted), LaTex formatte

### Chiral Perturbation Theory with tensor sources

We construct the most general chirally-invariant Lagrangian for mesons in the
presence of external sources coupled to the tensor current
\bar{\psi}\sigma_{\mu\nu}\psi. In order to have only even terms in the chiral
expansion, we consider the new source of O(p^2). With this choice, we build the
even-parity effective Lagrangian up to the p^6-order (NLO). While there are
only 4 new terms at the p^4-order, at p^6-order we find 78 terms for n_f=2 and
113 terms for n_f=3. We provide a detailed discussion on the different
mechanisms that ensure that our final set of operators is complete and
non-redundant. We also examine the odd-parity sector, to conclude that the
first operators appear at the p^8-order (NNLO).Comment: 23 pages, one figure; typos corrected, one paragraph added, new
section added, references added, published versio

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