1,591 research outputs found
Gluon Shadowing and Heavy Flavor Production off Nuclei
Gluon shadowing which is the main source of nuclear effects for production of
heavy flavored hadrons, remains unknown. We develop a light-cone dipole
approach aiming at simplifying the calculations of nuclear shadowing for heavy
flavor production, as well as the cross section which does not need
next-to-leading and higher order corrections. A substantial process dependence
of gluon shadowing is found at the scale of charm mass manifesting a deviation
from QCD factorization. The magnitude of the shadowing effect correlates with
the symmetry properties and color state of the produced c-cbar pair. It is
about twice as large as in DIS, but smaller than for charmonium production. The
higher twist shadowing correction related to a nonzero size of the c-cbar pair
is not negligible and steeply rises with energy. We predict an appreciable
suppression by shadowing for charm production in heavy ion collisions at RHIC
and a stronger effect at LHC. At the same time, we expect no visible difference
between nuclear effects for minimal bias and central collisions, as is
suggested by recent data from the PHENIX experiment at RHIC. We also
demonstrate that at medium high energies when no shadowing is possible, final
state interaction may cause a rather strong absorption of heavy flavored
hadrons produced at large x_F.Comment: Preprint NSF-ITP-02-40, ITP, UCSB, Santa Barbara; Latex 52 pages and
8 figure
Long-Range Coulomb Forces in DIS: Missed Radiative Corrections?
The Born approximation, one photon exchange, used for DIS is subject to
virtual radiative corrections which are related to the long-range Coulomb
forces. They may be sizeable for heavy nuclei since Z\alpha is not a small
parameter. So far these corrections are known only for two processes, elastic
scattering and bremsstrahlung on the Coulomb field of a point-like target.
While the former amplitude acquires only a phase, in the latter case the cross
section is modified also. Although the problem of Coulomb corrections for DIS
on nuclei is extremely difficult, it should be challenged rather than 'swept
under the carpet'. The importance of these radiative corrections is questioned
in present paper. We show that in the simplest case of a constant hadronic
current the Coulomb corrections provide a phase to the Born amplitude,
therefore the cross section remains the same. Inclusion of more realistic
hadronic dynamics changes this conclusion. The example of coherent production
of vector mesons off nuclei reveals large effects. So far a little progress has
been made deriving exact lepton wave functions in the Coulomb field of an
extended target. Employing available results based on the first-order
approximation in Z\alpha, we conclude that the Coulomb corrections are still
important for heavy nuclei. We also consider an alternative approach for
extended nuclear targets, the eikonal approximation, which we demonstrate to
reproduce the known exact results for Coulomb corrections. Calculating
electroproduction of vector mesons we again arrive at a large deviation from
the Born approximation. We conclude that one should accept with caution the
experimental results for nuclear effects in DIS based on analyses done in the
Born approximation.Comment: 24 pages including 4 figures. Fig.4 is modified and stylistic
corrections are made. The final version to appear in Eur.Phys.J.
Fractional Derivative as Fractional Power of Derivative
Definitions of fractional derivatives as fractional powers of derivative
operators are suggested. The Taylor series and Fourier series are used to
define fractional power of self-adjoint derivative operator. The Fourier
integrals and Weyl quantization procedure are applied to derive the definition
of fractional derivative operator. Fractional generalization of concept of
stability is considered.Comment: 20 pages, LaTe
Psi-Series Solution of Fractional Ginzburg-Landau Equation
One-dimensional Ginzburg-Landau equations with derivatives of noninteger
order are considered. Using psi-series with fractional powers, the solution of
the fractional Ginzburg-Landau (FGL) equation is derived. The leading-order
behaviours of solutions about an arbitrary singularity, as well as their
resonance structures, have been obtained. It was proved that fractional
equations of order with polynomial nonlinearity of order have the
noninteger power-like behavior of order near the singularity.Comment: LaTeX, 19 pages, 2 figure
Fractional Generalization of Gradient Systems
We consider a fractional generalization of gradient systems. We use
differential forms and exterior derivatives of fractional orders. Examples of
fractional gradient systems are considered. We describe the stationary states
of these systems.Comment: 11 pages, LaTe
Fractional Variations for Dynamical Systems: Hamilton and Lagrange Approaches
Fractional generalization of an exterior derivative for calculus of
variations is defined. The Hamilton and Lagrange approaches are considered.
Fractional Hamilton and Euler-Lagrange equations are derived. Fractional
equations of motion are obtained by fractional variation of Lagrangian and
Hamiltonian that have only integer derivatives.Comment: 21 pages, LaTe
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