6,356 research outputs found
Erratum: Solution of periodic Poisson's equation and the Hartree-Fock approach for solids with extended electron states: application to linear augmented plane wave method
Erratum to Int. J. Quantum Chem. v. 89, pp. 57-85 (2002)Comment: 1 pag
The Running BFKL: Resolution of Caldwell's Puzzle
The HERA data on the proton structure function, , at very small
and show the dramatic departure of the logarithmic slope, , from theoretical predictions based on the DGLAP
evolution. We show that the running BFKL approach provides the quantitative
explanation for the observed and/or -dependence of .Comment: 7 pages, Latex, 4 Figures, P
The hard scale in the exclusive rho-meson production in diffractive DIS
We re-examine the issue of the pQCD factorization scale in the exclusive rho
production in diffractive DIS from the k_t-factorization point of view. We find
that this scale differs significantly from, and possesses much flatter Q^2
behavior than widely used value (Q^2 + m_\rho^2)/4. With these results in mind,
we discuss the Q^2 shape of the rho meson production cross section. We
introduce rescaled cross sections, which might provide further insight into the
dynamics of rho production. We also comment on the recent ZEUS observation of
energy-independent ratio sigma(gamma* p --> rho p) / sigma_{tot}(gamma*p).Comment: 14 pages, 7 eps figure
On dark matter search after DAMA with Ge-73
The Weakly Interacting Massive Particle (WIMP) is one of the main candidates
for the relic dark matter (DM).In the effective low-energy minimal
supersymmetric standard model (effMSSM) the neutralino-nucleon spin and scalar
cross sections in the low-mass regime were calculated. The calculated cross
sections are compared with almost all experimental currently available
exclusion curves for spin-dependent WIMP-proton and WIMP-neutron cross
sections. It is demonstrated that in general about two-orders-of-magnitude
improvement of the current DM experiment sensitivities is needed to reach the
(effMSSM) SUSY predictions. At the current level of accuracy it looks
reasonable to safely neglect sub-dominant spin WIMP-nucleon contributions
analyzing the data from spin-non-zero targets. To avoid misleading
discrepancies between data and SUSY calculations it is, however, preferable to
use a mixed spin-scalar coupling approach.This approach is applied to estimate
future prospects of experiments with the odd-neutron high-spin isotope Ge-73.
It is noticed that the DAMA evidence favors the light Higgs sector in the
effMSSM, a high event rate in a Ge-73 detector and relatively high upgoing muon
fluxes from relic neutralino annihilations in the Earth and the Sun.Comment: 29 pages, 12 figures, 124 reference
Breaking of k_\perp-factorization for Single Jet Production off Nuclei
The linear k_\perp-factorization is part and parcel of the pQCD description
of high energy hard processes off free nucleons.
In the case of heavy nuclear targets the very concept of nuclear parton
density becomes ill-defined as exemplified by the recent derivation [2] of
nonlinear nuclear k_\perp-factorization for forward dijet production in DIS off
nuclei. Here we report a derivation of the related breaking of
k_\perp-factorization for single-jet processes. We present a general formalism
and apply it to several cases of practical interest: open charm and quark and
gluon jet production in the central to beam fragmentation region of
\gamma^*p,\gamma^*A, pp and pA collisions. We show how the pattern of
k_\perp-factorization breaking and the nature and number of exchanged nuclear
pomerons do change within the phase space of produced quark and gluon jets. As
an application of the nonlinear k_\perp-factorization we discuss the Cronin
effect. Our results are also applicable to the p_\perp-dependence of the
Landau-Pomeranchuk-Migdal effect for, and nuclear quenching of, jets produced
in the proton hemisphere of pA collisions.Comment: 55 pages, 9 eps figures, presentation shortened, a number of typos
removed, to appear in Phys. Rev.
Quenching of Leading Jets and Particles: the p_t Dependent Landau-Pomeranchuk-Migdal effect from Nonlinear k_t Factorization
We report the first derivation of the Landau-Pomeranchuk-Migdal effect for
leading jets at fixed values of the transverse momentum p_t in the beam
fragmentation region of hadron-nucleus collisions from RHIC (Relativistic Heavy
Ion Collider) to LHC (Large Hadron Collider). The major novelty of this work is
a derivation of the missing virtual radiative pQCD correction to these
processes - the real-emission radiative corrections are already available in
the literature. We manifestly implement the unitarity relation, which in the
simplest form requires that upon summing over the virtual and real-emission
corrections the total number of scattered quarks must exactly equal unity. For
the free-nucleon target, the leading jet spectrum is shown to satisfy the
familiar linear Balitsky-Fadin-Kuraev-Lipatov leading log(1/x) (LL-1/x)
evolution. For nuclear targets, the nonlinear k_t-factorization for the LL-1/x
evolution of the leading jet sepctrum is shown to exactly match the equally
nonlinear LL-1/x evolution of the collective nuclear glue - there emerges a
unique linear k_t-factorization relation between the two nonlinear evolving
nuclear observables. We argue that within the standard dilute uncorrelated
nucleonic gas treatment of heavy nuclei, in the finite energy range from RHIC
to LHC, the leading jet spectrum can be evolved in the LL-1/x
Balitsky-Kovchegov approximation. We comment on the extension of these results
to, and their possible reggeon field theory interpretation for, mid-rapidity
jets at LHC.Comment: 36 pages, 8 eps figs, revised, discussion on reggeon interpretation
and refs. adde
Nonlinear kT factorization for Forward Dijets in DIS off Nuclei in the Saturation Regime
We develop the QCD description of the breakup of photons into forward dijets
in small-x deep inelastic scattering off nuclei in the saturation regime. Based
on the color dipole approach, we derive a multiple scattering expansion for
intranuclear distortions of the jet-jet transverse momentum spectrum. A special
attention is paid to the non-Abelian aspects of the propagation of color
dipoles in a nuclear medium. We report a nonlinear -factorization
formula for the breakup of photons into dijets in terms of the collective
Weizs\"acker-Williams (WW) glue of nuclei as defined in ref.
\cite{Saturation,NSSdijet}. For hard dijets with the transverse momenta above
the saturation scale the azimuthal decorrelation (acoplanarity) momentum is of
the order of the nuclear saturation momentum QA. For minijets with the
transverse momentum below the saturation scale the nonlinear kT-factorization
predicts a complete disappearance of the jet-jet correlation. We comment on a
possible relevance of the nuclear decorrelation of jets to the experimental
data from the STAR-RHIC Collaboration.Comment: 40 pages, 7 figure
Non-linear BFKL dynamics: color screening vs. gluon fusion
A feasible mechanism of unitarization of amplitudes of deep inelastic
scattering at small values of Bjorken is the gluon fusion. However, its
efficiency depends crucially on the vacuum color screening effect which
accompanies the multiplication and the diffusion of BFKL gluons from small to
large distances. From the fits to lattice data on field strength correlators
the propagation length of perturbative gluons is fermi. The
probability to find a perturbative gluon with short propagation length at large
distances is suppressed exponentially. It changes the pattern of (dif)fusion
dramatically. The magnitude of the fusion effect appears to be controlled by
the new dimensionless parameter , with the diffraction cone
slope standing for the characteristic size of the interaction region. It
should slowly decrease at large . Smallness of the
ratio makes the non-linear effects rather weak even at lowest
Bjorken available at HERA. We report the results of our studies of the
non-linear BFKL equation which has been generalized to incorporate the running
coupling and the screening radius as the infrared regulator.Comment: 16 pages, 2 figures, version accepted for publication, references
adde
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