6,071 research outputs found
Diffractive photoproduction of heavy quarks in hadronic collisions
In this letter we study the diffractive photoproduction of heavy quarks in
hadronic (pp/pA/AA) interactions for Tevatron and LHC energies. The integrated
cross section and rapidity distribution for the process h_1 h_2 --> h_1 h_2
QQBAR (h_i = p,A and Q = c,b) are estimated using the Color Glass Condensate
(CGC) formalism. Our results indicate that this production channel has larger
cross sections than the competing reactions of double diffractive production
and coherent AA reactions initiated by two-photon collisions.Comment: 4 pages, 2 figures, 1 table. Version to be published in Physical
Review
Photoproduction of mesons in ultraperipheral heavy ion collisions at energies available at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC)
We investigate the photoproduction of mesons in ultraperipheral heavy
ion collisions at RHIC and LHC energies in the dipole approach and within two
phenomenological models based on the the Color Glass Condensate (CGC)
formalism. We estimate the integrated cross section and rapidity distribution
for meson production and compare our predictions with the data from the STAR
collaboration. In particular, we demonstrate that the total cross section at
RHIC is strongly dependent on the energy behavior of the dipole-target cross
section at low energies, which is not well determined in the dipole approach.
In contrast, the predictions at midrapidities at RHIC and in the full rapidity
at LHC are under theoretical control and can be used to test the QCD dynamics
at high energies.Comment: 6 pages, 5 figures, 1 table. Improved version to be published in
Physical Review
No-horizon theorem for spacetimes with spacelike G1 isometry groups
We consider four-dimensional spacetimes which obey the
Einstein equations , and admit a global spacelike
isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
which guarantees that cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for -symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.Comment: 8 pages, LaTeX, uses IOP package; published in Class. Quantum Gra
The AGL Equation from the Dipole Picture
The AGL equation includes all multiple pomeron exchanges in the double
logarithmic approximation (DLA) limit, leading to an unitarized gluon
distribution in the small x regime. This equation was originally obtained using
the Glauber-Mueller approach. We demonstrate in this paper that the AGL
equation and, consequently, the GLR equation, can also be obtained from the
dipole picture in the double logarithmic limit, using an evolution equation,
recently proposed, which includes all multiple pomeron exchanges in the leading
logarithmic approximation. Our conclusion is that the AGL equation is a good
candidate for an unitarized evolution equation at small x in the DLA limit.Comment: 16 pages, 2 figures. Accepted for publication in Nuc. Phys.
A note on the cylindrical collapse of counter-rotating dust
We find analytical solutions describing the collapse of an infinitely long
cylindrical shell of counter-rotating dust. We show that--for the classes of
solutions discussed herein--from regular initial data a curvature singularity
inevitably develops, and no apparent horizons form, thus in accord with the
spirit of the hoop conjecture.Comment: 8 pages, LaTeX, ijmpd macros (included), 1 eps figure; accepted for
publication in Int. J. Mod. Phys.
Some Aspects of the Exact Foldy-Wouthuysen Transformation for a Dirac Fermion
The Foldy-Wouthuysen transformation (FWT) is used to separate distinct
components of relativistic spinor field, e.g. electron and positron. Usually,
the FWT is perturbative, but in some cases there is an involution operator and
the transformation can be done exactly. We consider some aspects of an exact
FWT and show that, even if the theory does not admit an involution operator,
one can use the technique of exact FWT to obtain the conventional perturbative
result. Several particular cases can be elaborated as examples
Gluon saturation and the Froissart bound: a simple approach
At very high energies we expect that the hadronic cross sections satisfy the
Froissart bound, which is a well-established property of the strong
interactions. In this energy regime we also expect the formation of the Color
Glass Condensate, characterized by gluon saturation and a typical momentum
scale: the saturation scale . In this paper we show that if a saturation
window exists between the nonperturbative and perturbative regimes of Quantum
Chromodynamics (QCD), the total cross sections satisfy the Froissart bound.
Furthermore, we show that our approach allows us to describe the high energy
experimental data on total cross sections.Comment: 6 pages, 5 figures. Includes additional figures, discussion and
reference
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