498 research outputs found
Non-Gaussian fluctuations near the QCD critical point
We study the effect of the QCD critical point on non-Gaussian moments
(cumulants) of fluctuations of experimental observables in heavy-ion
collisions. We find that these moments are very sensitive to the proximity of
the critical point, as measured by the magnitude of the correlation length xi.
For example, the cubic central moment of multiplicity ~ xi^4.5 and the quartic
cumulant ~ xi^7. We estimate the magnitude of critical point contributions to
non-Gaussian fluctuations of pion and proton multiplicities.Comment: 4 pages, 3 figure
Hydro+: hydrodynamics with parametric slowing down and fluctuations near the critical point
The search for the QCD critical point in heavy-ion collision experiments
requires dynamical simulations of the bulk evolution of QCD matter as well as
of fluctuations. We consider two essential ingredients of such a simulation: a
generic extension of hydrodynamics by a_parametrically_ slow mode or modes
("Hydro+") and a description of fluctuations out of equilibrium. By combining
the two ingredients we are able to describe the bulk evolution and the
fluctutations within the same framework. Critical slowing down means that
equilibration of fluctuations could be as slow as hydrodynamic evolution and
thus fluctuations could significantly deviate from equilibrium near the
critical point. We generalize hydrodynamics to partial-equilibrium conditions
where the state of the system is characterized by the off-equilibrium magnitude
of fluctuations in addition to the usual hydrodynamic variables -- conserved
densities. We find that the key element of the new formalism -- the extended
entropy taking into account the off-equilibrium fluctuations -- is remarkably
similar to the 2PI action in quantum field theory. We show how the new Hydro+
formalism reproduces two major effects of critical fluctuations on the bulk
evolution: the strong frequency dependence of the anomalously large bulk
viscosity as well as the stiffening of the equation of state with increasing
frequency or wave-number. While the agreement with known results confirms its
validity, the fact that Hydro+ achieves this within a local and deterministic
framework gives it significant advantages for dynamical simulations.Comment: 46 pages, 5 figure
Proton number fluctuation as a signal of the QCD critical end-point
We argue that the event-by-event fluctuation of the proton number is a
meaningful and promising observable for the purpose of detecting the QCD
critical end-point in heavy-ion collision experiments. The long range
fluctuation of the order parameter induces a characteristic correlation between
protons which can be measured. The proton fluctuation also manifests itself as
anomalous enhancement of charge fluctuations near the end-point, which might be
already seen in existing data.Comment: 4 pages, version accepted in PR
Dynamic universality class of the QCD critical point
We show that the dynamic universality class of the QCD critical point is that
of model H and discuss the dynamic critical exponents. We show that the baryon
diffusion rate vanishes at the critical point. The dynamic critical index
is close to 3.Comment: 12 pages. To be published in PRD. Appendix about isospin density
added, introduction expande
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