123 research outputs found
Do nuclear collisions create a locally equilibrated quark-gluon plasma?
Experimental results on azimuthal correlations in high energy nuclear
collisions (nucleus-nucleus, proton-nucleus and proton-proton) seem to be well
described by viscous hydrodynamics. It is often argued that this agreement
implies either local thermal equilibrium or at least local isotropy. In this
note, I present arguments why this is not the case. Neither local
near-equilibrium nor near-isotropy are required in order for hydrodynamics to
offer a successful and accurate description of experimental results. However, I
predict the breakdown of hydrodynamics at momenta of order seven times the
temperature, corresponding to a smallest possible QCD liquid drop size of 0.15
fm.Comment: 14 pages, 6 figures; v2: references added, major changes in section
VI, qualitative conclusions unchanged; v3: minor typos fixed, matches
published versio
Cold deconfined matter EOS through an HTL quasi-particle model
Using quasi-particle models, lattice data can be mapped to finite chemical
potential. By comparing a simple and an HTL quasi-particle model, we derive the
general trend that a full inclusion of the plasmon effect will give.Comment: 5 pages, 6 figures, contribution to the conference Strong and
Electroweak Matter (SEWM2002), Heidelberg, Germany, October 2-5, 2002; v2:
plots and references update
Relativistic Hydrodynamic Attractors with Broken Symmetries: Non-Conformal and Non-Homogeneous
Standard textbooks will state that hydrodynamics requires near-equilibrium to
be applicable. Recently, however, out-of-equilibrium attractor solutions for
hydrodynamics have been found in kinetic theory and holography in systems with
a high degree of symmetry, suggesting the possibility of a genuine
out-of-equilibrium formulation of hydrodynamics. This work demonstrates that
attractor solutions also occur in non-conformal kinetic theory and spatially
non-homogeneous systems, potentially having important implications for the
interpretation of experimental data in heavy-ion and proton-proton collisions
and relativistic fluid dynamics as a whole.Comment: 13 pages, 2 figures; v2: minor changes (typos, etc.); v3: matches
published versio
Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport
In the limit of short mean free path, relativistic kinetic theory gives rise
to hydrodynamics through a systematically improvable gradient expansion. In the
present work, a systematically improvable expansion in the opposite limit of
large mean free path is considered, describing the dynamics of particles which
are almost, but not quite, non-interacting. This non-hydrodynamic "eremitic"
expansion does not break down for large gradients, and may be useful in
situations where a hydrodynamic treatment is not applicable. As applications,
azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions
at TeV are calculated from the first order eremitic expansion
of kinetic theory in the relaxation time approximation.Comment: 26 pages, 5 figures; v2: reference to Borghini and Gombeaud added who
discussed same setup in 2010, typos corrected; v3: minor changes, matches
published versio
Light-Heavy Ion Collisions: A window into pre-equilibrium QCD dynamics?
Relativistic collisions of light on heavy ions (p+Au at sqrt(s)=7.7 GeV,
p+Au, d+Au,3He+Au at sqrt(s)=62.4 GeV and 200 GeV and p+Pb, 3He+Pb at
sqrt(s)=5.02 TeV) are simulated using "superSONIC", a model that includes
pre-equilibrium flow, viscous hydrodynamics and a hadronic cascade afterburner.
Even though these systems have strong gradients and only consist of at most a
few tens of charged particles per unit rapidity, one finds evidence that a
hydrodynamic description applies to these systems. Based on these simulations,
the presence of a triangular flow component in d+Au collisions at sqrt(s)=200
GeV is predicted to be similar in magnitude to that found in 3He+Au collisions.
Furthermore, the v3(p_T) ratio of 3He+Au to d+Au is found to be sensitive to
the presence of pre-equilibrium flow. This would imply an experimentally
accessible window into pre-equilibrium QCD dynamics using light-heavy ion
collisions.Comment: 8 pages plus appendix; 9 figure
Collective flow without hydrodynamics: simulation results for relativistic ion collisions
Flow signatures in experimental data from relativistic ion collisions are
usually interpreted as a fingerprint of the presence of a hydrodynamic phase
during the evolution of these systems. In this work, flow signatures arising
from event-by-event viscous hydrodynamics are compared to those arising from
event-by-event non-interacting particle dynamics (free-streaming), both
followed by a late-stage hadronic cascade, in d+Au, 3He+Au at sqrt(s)=200 GeV
and p+Pb collisions at sqrt(s)=5 TeV, respectively. For comparison, also Pb+Pb
collisions at sqrt(s)=2.76 TeV are simulated. It is found that non-hydrodynamic
evolution can give rise to equal or larger radial flow than hydrodynamics with
eta/s=0.08 in all simulated collision systems. In light-on-heavy-ion
collisions, free-streaming gives rise to triangular and quadrupolar flow
comparable to or larger than that from hydrodynamics, but it generally leads to
considerably smaller elliptic flow. As expected, free-streaming leads to
considerably less elliptic, triangular and quadrupolar flow than hydrodynamics
in nucleus-nucleus collisions, such as event-by-event Pb+Pb collisions at
sqrt(s)=2.76 TeV.Comment: 18 pages; 9 figures; v2: minor errors corrected, HBT radii added; v3:
added subsection on radial flow breakdown in peripheral p+Pb, matches
published versio
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