159 research outputs found
Theory Summary: International Symposium on Multiparticle Dynamics 2008
I summarize the theory talks presented at the International Symposium on
Multiparticle Dynamics 2008.Comment: 20 pages, 16 figures; v2: reference added; v3: typos correcte
Classical Initial Conditions for Nucleus-Nucleus Collisions
We present the results of an analytical calculation of the distribution of
gluons in the state immediately following a heavy ion collision in the
quasi-classical limit of QCD given by McLerran-Venugopalan model. We show that
the typical transverse energy Et of the produced gluons is of the order of the
saturation scale of the nuclei Qs, as predicted by Mueller. We demonstrate that
due to multiple rescatterings the obtained gluon distribution remains finite
(up to logarithms of k) in the soft transverse momentum limit of k << Q_s. We
compare the gluon spectrum in the single nuclear wave function before the
collision to the spectrum of the produced gluons. The total number of produced
gluons turns out to be proportional to the total number of gluons inside the
nuclear wave function before the collision with the proportionality coefficient
c = 2 ln 2.Comment: 4 pages, 3 figures, to appear in the Proceedings of 15th
International Conference on Ultrarelativistic Nucleus-Nucleus Collisions
(QM2001), Stony Brook, New York, 15-20 Jan 200
Running Coupling Evolution for Diffractive Dissociation and the NLO Odderon Intercept
We summarize the results of including running coupling corrections into the
nonlinear evolution equation for diffractive dissociation. We also document a
prediction that the NLO QCD odderon intercept is zero resulting from a
discussion at the Diffraction 2012 Workshop.Comment: 4 pages, 1 figure; contains an original prediction embedded in the
Diffraction 2012 proceedings; v2: minor corrections include
Shock Wave Collisions and Thermalization in AdS_5
We study heavy ion collisions at strong 't Hooft coupling using AdS/CFT
correspondence. According to the AdS/CFT dictionary heavy ion collisions
correspond to gravitational shock wave collisions in AdS_5. We construct the
metric in the forward light cone after the collision perturbatively through
expansion of Einstein equations in graviton exchanges. We obtain an analytic
expression for the metric including all-order graviton exchanges with one shock
wave, while keeping the exchanges with another shock wave at the lowest order.
We read off the corresponding energy-momentum tensor of the produced medium.
Unfortunately this energy-momentum tensor does not correspond to ideal
hydrodynamics, indicating that higher order graviton exchanges are needed to
construct the full solution of the problem. We also show that shock waves must
completely stop almost immediately after the collision in AdS_5, which, on the
field theory side, corresponds to complete nuclear stopping due to strong
coupling effects, likely leading to Landau hydrodynamics. Finally, we perform
trapped surface analysis of the shock wave collisions demonstrating that a bulk
black hole, corresponding to ideal hydrodynamics on the boundary, has to be
created in such collisions, thus constructing a proof of thermalization in
heavy ion collisions at strong coupling.Comment: 10 pages, 6 figures, based on talks given at the Symposium on High
Energy Strong Interactions 2010 (HESI 2010), Yukawa Institute for Theoretical
Physics, Kyoto, Japan, August 9-13, 2010, and at the 4th International
Conference on Hard and Electromagnetic Probes of High Energy Nuclear
Collisions (Hard Probes 2010), Eilat, Israel, October 10-15, 201
High Energy QCD and the Large Nc Limit
We review recent progress in understanding QCD at high energies and the role
played in it by the large Nc limit. We discuss unitarization of total hadronic
cross sections and saturation of structure functions at high energies.Comment: 20 pages, 8 figures, to be published in the proceedings of "The
Phenomenology of Large Nc QCD" workshop, 9-11 January 2002, Arizona State
University, Tempe, A
Orbital Angular Momentum at Small
We determine the small Bjorken asymptotics of the quark and gluon orbital
angular momentum (OAM) distributions in the proton in the double-logarithmic
approximation (DLA), which resums powers of with
the strong coupling constant. Starting with the operator definitions
for the quark and gluon OAM, we simplify them at small , relating them,
respectively, to the polarized dipole amplitudes for the quark and gluon
helicities defined in our earlier works. Using the small- evolution
equations derived for these polarized dipole amplitudes earlier we arrive at
the following small- asymptotics of the quark and gluon OAM distributions in
the large- limit:
\begin{align}
L_{q + \bar{q}} (x, Q^2) = - \Delta \Sigma (x, Q^2) \sim
\left(\frac{1}{x}\right)^{\frac{4}{\sqrt{3}} \, \sqrt{\frac{\alpha_s
\, N_c}{2 \pi}} }, \ \ \ \ \
L_G (x, Q^2) \sim \Delta G (x, Q^2) \sim
\left(\frac{1}{x}\right)^{\frac{13}{4 \sqrt{3}} \, \sqrt{\frac{\alpha_s
\, N_c}{2 \pi}}} . \end{align}Comment: 27 page
Isotropization and Thermalization in Heavy Ion Collisions
We argue that isotropization and, consequently, thermalization of the system
of gluons and quarks produced in an ultrarelativistic heavy ion collision does
not follow from Feynman diagram analysis to any order in the coupling constant.
We conclude that the apparent thermalization of quarks and gluons, leading to
success of perfect fluid hydrodynamics in describing heavy ion collisions at
RHIC, can only be attributed to the non-perturbative QCD effects not captured
by Feynman diagrams.
We proceed by modeling these non-pertrubative thermalization effects using
viscous hydrodynamics. We point out that matching Color Glass Condensate inital
conditions with viscous hydrodynamics leads to continuous evolution of all
components of energy-momentum tensor and, unlike the case of ideal
hydrodynamics, does not give a discontinuity in the longitudinal pressure. An
important consequence of such a matching is a relationship between the
thermalization time and shear viscosity: we observe that small viscosity leads
to short thermalization time.Comment: Includes new results. 8 pages, 1 figure, based on proceedings
contributions at "Quark Matter 2005" conference in Budapest, Hungary, August
4-9, 2005 and at the workshop on "Quark-Gluon Plasma Thermalization" in
Vienna, Austria, August 10-12, 200
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