52 research outputs found
Non-perturbative gluodynamics of high energy heavy-ion collisions
The dynamics of low-x partons in the transverse plane of a high-energy
nuclear collision is classical, and therefore admits a fully non--perturbative
numerical treatment. We report results of a recent study estimating the initial
energy density in the central region of a collision. Preliminary estimates of
the number of gluons per unit rapidity, and the initial transverse momentum
distribution of gluons, are also provided.Comment: Latex,9 pages, 4 figures, invited talk at 5th workshop on QCD
(QCD2000), Villefrance-sur-Mer, Jan.3rd-7th, 2000; minor typo correcte
Small x physics and the initial conditions in heavy ion collisions
At very high energies, the high parton densities (characterized by a
semi-hard saturation scale \Lambda_s) ensure that parton distributions can be
described by a classical effective field theory with remarkable properties
analogous to those of spin glass systems. This color glass condensate (CGC) of
gluons also provides the initial conditions for multi-particle production in
high energy nuclear collisions. In this talk, we briefly summarize recent
theoretical and phenomenological progress in the CGC approach to small x
physics. In particular, we discuss recent numerical work on the real time
gluodynamics of partons after a nuclear collision. The implications of this
work for the theoretical study of thermalization in nuclear collisions and on
the phenomenological interpretation of results of the recent RHIC experiments
are also discussed.Comment: LaTex, 8 pages. Plenary talk by RV at Quark Matter 2001, Stony Brook,
USA and at Workshop on Lepton Scattering, Hadrons, and QCD, CSSM, Adelaide,
Australi
Classical Gluodynamics of High Energy Nuclear Collisions: an Erratum and an Update
We comment on the relation of our previous work on the classical gluodynamics
of high energy nuclear collisions to recent work by Lappi (hep-ph/0303076).
While our results for the non-perturbative number liberation coefficient agree,
those for the energy disagree by a factor of 2. This discrepancy can be traced
to an overall normalization error in our non-perturbative formula for the
energy. When corrected for, all previous results are in excellent agreement
with those of Lappi. The implications of the results of these two independent
computations for RHIC phenomenology are noted.Comment: 6 pages, 2 figure
Elliptic Flow from Color Glass Condensate
We show that an observable fraction of the measured elliptic flow may
originate in classical gluon fields at the initial stage of a peripheral
high-energy nuclear collision. This mechanism complements the contribution of
late stage mechanisms, such as those described by hydrodynamics, to the
observed elliptic flow.Comment: 4 pages, 2 figures, talk contributed to Quark Matter-2002 conference
(Nantes, France, July 2002
Elliptic flow of colored glass in high energy heavy ion collisions
We compute the elliptic flow generated by classical gluon fields in a high
energy nuclear collision. The classical gluon fields are described by a typical
momentum scale, the saturation scale Lambda_s, which is, for RHIC energies, of
the order of 1-2 GeV. A significant elliptic flow is generated only over time
scales on the order of the system size R. The flow is dominated by soft modes
which linearize at very late times . We discuss the implications of our result for the theoretical
interpretation of the RHIC data.Comment: 5 pages, 4 figures, extend discussions and add reference
Gluon production in the Color Glass Condensate model of collisions of ultrarelativistic finite nuclei
We extend previous work on high energy nuclear collisions in the Color Glass
Condensate model to study collisions of finite ultrarelativistic nuclei. The
changes implemented include a) imposition of color neutrality at the nucleon
level and b) realistic nuclear matter distributions of finite nuclei.
The saturation scale characterizing the fields of color charge is explicitly
position dependent, . We compute gluon distributions
both before and after the collisions. The gluon distribution in the nuclear
wavefunction before the collision is significantly suppressed below the
saturation scale when compared to the simple McLerran-Venugopalan model
prediction, while the behavior at large momentum remains
unchanged. We study the centrality dependence of produced gluons and compare it
to the centrality dependence of charged hadrons exhibited by the RHIC data. We
demonstrate the geometrical scaling property of the initial gluon transverse
momentum distributions for different centralities. Classical Yang-Mills results
for are simply matched to perturbative QCD computations for
-the resulting energy per particle is significantly lower than
the purely classical estimates. Our results for nuclear collisions can be used
as initial conditions for quantitative studies of the further evolution and
possible equilibration of hot and dense gluonic matter produced in heavy ion
collisions. Finally, we study collisions within the classical framework.
Our results agree well with previously derived analytical results in the
appropriate kinematical regions.Comment: 13 pages, 9 figure
Quantum phase transitions in cascading gauge theory
We study a ground state of N=1 supersymmetric SU(K+P) x SU(K) cascading gauge
theory of Klebanov et.al [1,2] on R x S^3 at zero temperature. A radius of S^3
sets a compactification scale mu. An interplay between mu and the strong
coupling scale Lambda of the theory leads to an interesting pattern of quantum
phases of the system. For mu > mu_cSB=1.240467(8)Lambda the ground state of the
theory is chirally symmetric. At mu=mu_cSB the theory undergoes the first-order
transition to a phase with spontaneous breaking of the chiral symmetry. We
further demonstrate that the chirally symmetric ground state of cascading gauge
theory becomes perturbatively unstable at scales below mu_c=0.950634(5)mu_cSB.
Finally, we point out that for mu < 1.486402(5)Lambda the stress-energy tensor
of cascading gauge theory can source inflation of a closed Universe.Comment: 62 pages, 9 figure
Short distance properties of cascading gauge theories
We study the short distance (large momentum) properties of correlation
functions of cascading gauge theories by performing a tree-level computation in
their dual gravitational background. We prove that these theories are
holographically renormalizable; the correlators have only analytic ultraviolet
divergences, which may be removed by appropriate local counterterms. We find
that n-point correlation functions of properly normalized operators have the
expected scaling in the semi-classical gravity (large N) limit: they scale as
N_{eff}^{2-n} with N_{eff} proportional to ln(k/Lambda) where k is a typical
momentum. Our analysis thus confirms the interpretation of the cascading gauge
theories as renormalizable four-dimensional quantum field theories with an
effective number of degrees of freedom which logarithmically increases with the
energy.Comment: 47 pages, no figure
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