4,192 research outputs found
Scattering Through QCD Sphalerons
Diffractive parton-parton scattering in the soft pomeron regime can be
explained by the production of a QCD sphaleron. Sphaleron production results
into the emission of gluons and quarks. At RHIC we expect many
sphalerons to be released thereby affecting most prompt processes.Comment: Contribution to quark matter 200
Chiral random matrix models: thermodynamics, phase transitions and universality
For one flavour, we observe that standard chiral random matrix models as inspired from QCD spin and color symmetry, are a simplified version of the Nambu-Jona-Lasinio (NJL) model whether in vacuum or matter. The ensuing thermodynamics is that of constituent quarks, with an entropy driven second-order transition and mean-field exponents. At zero temperature but finite chemical potential \mu, the transition is first order, with a critical \mu of the order of the constituent quark mass. The transition occurs at zero baryon density, since chiral random matrix models do not support a Fermi surface. For two and three flavours non-standard chiral random matrix models with U_A(1) breaking are suggested, with mean-field phase transitions in large N. For three flavours and small current masses (weak field), the chiral random matrix model exhibits a first order transition remiscent of the isotropic-nematic transition in liquid crystals. The latter displays a tricritical point for strong fields. Some issues related to confinement are briefly discussed
Summing free unitary random matrices
I use quaternion free probability calculus - an extension of free probability
to non-Hermitian matrices (which is introduced in a succinct but self-contained
way) - to derive in the large-size limit the mean densities of the eigenvalues
and singular values of sums of independent unitary random matrices, weighted by
complex numbers. In the case of CUE summands, I write them in terms of two
"master equations," which I then solve and numerically test in four specific
cases. I conjecture a finite-size extension of these results, exploiting the
complementary error function. I prove a central limit theorem, and its first
sub-leading correction, for independent identically-distributed zero-drift
unitary random matrices.Comment: 17 pages, 15 figure
Relaxation mechanisms of the persistent spin helix
We study the lifetime of the persistent spin helix in semiconductor quantum
wells with equal Rashba- and linear Dresselhaus spin-orbit interactions. In
order to address the temperature dependence of the relevant spin relaxation
mechanisms we derive and solve semiclassical spin diffusion equations taking
into account spin-dependent impurity scattering, cubic Dresselhaus spin-orbit
interactions and the effect of electron-electron interactions. For the
experimentally relevant regime we find that the lifetime of the persistent spin
helix is mainly determined by the interplay of cubic Dresselhaus spin-orbit
interaction and electron-electron interactions. We propose that even longer
lifetimes can be achieved by generating a spatially damped spin profile instead
of the persistent spin helix state.Comment: 12 pages, 2 figure
QCD Saturation Equations including Dipole-Dipole Correlation
We derive two coupled non-linear evolution equations corresponding to the
truncation of the Balitsky infinite hierarchy of saturation equations after
inclusion of dipole-dipole correlations, i.e. one step beyond the
Balitsky-Kovchegov (BK) equation. We exhibit an exact solution for maximal
correlation which still satisfies the same asymptotic geometric scaling as BK
but with the S-matrix going to 1/2 (instead of 0) in the full saturation
region.Comment: 4 pages, no figure. Comment, references and acknowledgment adde
Unified description of Bjorken and Landau 1+1 hydrodynamics
We propose a generalization of the Bjorken in-out Ansatz for fluid
trajectories which, when applied to the (1+1) hydrodynamic equations, generates
a one-parameter family of analytic solutions interpolating between the
boost-invariant Bjorken picture and the non boost-invariant one by Landau. This
parameter characterises the proper-time scale when the fluid velocities
approach the in-out Ansatz. We discuss the resulting rapidity distribution of
entropy for various freeze-out conditions and compare it with the original
Bjorken and Landau results.Comment: 20 pages, 5 figure
High energy amplitude as an admixture of "soft" and "hard" Pomerons
In this paper an attempt is made to find an interface of the perturbative
BFKL Pomeron with the non-perturbative Pomeron originating from
non-perturbative QCD phenomena such as QCD instantons and/or scale anomaly. The
main idea is that the non-perturbative Pomeron involves a large scale (), which is larger than the scale from which perturbative QCD is
applicable. One key result is that even for processes involving a large hard
scale (such as DIS) the low behavior is determined by an effective Pomeron
with an intercept having an essential non-perturbative QCD contribution.Comment: 29 pages, 13 fugures. Accepted for publication in Nucl. Phys.
On semiclassical calculation of three-point functions in AdS_5 \times T^(1,1)
Recently there has been progress on the computation of two- and three-point
correlation functions with two "heavy" states via semiclassical methods. We
extend this analysis to the case of AdS_5 \times T^(1,1), and examine the
suggested procedure for the case of several simple string solutions. By making
use of AdS/CFT duality, we derive the relevant correlation functions of
operators belonging to the dual gauge theory.Comment: 18 pages, added referenc
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