13 research outputs found
Effective description of dark matter as a viscous fluid
Treating dark matter at large scales as an effectively viscous fluid provides
an improved framework for the calculation of the density and velocity power
spectra compared to the standard assumption of an ideal pressureless fluid. We
discuss how this framework can be made concrete through an appropriate
coarse-graining procedure. We also review results that demonstrate that it
improves the convergence of cosmological perturbation theory.Comment: 8 pages, 3 figures, talk by N. Tetradis at Quarks-2016, includes
unpublished materia
Turbulent fluctuations around Bjorken flow
We study the evolution of local event-by-event deviations from smooth average
fluid dynamic fields, as they can arise in heavy ion collisions from the
propagation of fluctuating initial conditions. Local fluctuations around
Bjorken flow are found to be governed by non-linear equations whose solutions
can be characterized qualitatively in terms of Reynolds numbers. Perturbations
at different rapidities decouple quickly, and satisfy (after suitable
coordinate transformations) an effectively two-dimensional Navier-Stokes
equation of non-relativistic form. We discuss the conditions under which
non-linearities in these equations cannot be neglected and turbulent behavior
is expected to set in.Comment: 4 pages, 2 figures - To appear in the conference proceedings for
Quark Matter 2011, May 23 - May 28, Annecy, Franc
Flow in heavy-ion collisions - Theory Perspective
I review recent developments in the field of relativistic hydrodynamics and
its application to the bulk dynamics in heavy-ion collisions at the
Relativistic Heavy- Ion Collider (RHIC) and the Large Hadron Collider (LHC). In
particular, I report on progress in going beyond second order relativistic
viscous hydrodynamics for conformal fluids, including temperature dependent
shear viscosity to entropy density ratios, as well as coupling hydrodynamic
calculations to microscopic hadronic rescattering models. I describe
event-by-event hydrodynamic simulations and their ability to compute higher
harmonic flow coefficients. Combined comparisons of all harmonics to recent
experimental data from both RHIC and LHC will potentially allow to determine
the desired details of the initial state and the medium properties of the
quark-gluon plasma produced in heavy-ion collisions.Comment: 8 pages, Invited plenary talk at the 22nd International Conference on
Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), May 23-28
2011, Annecy, Franc
Fluctuations around Bjorken Flow and the onset of turbulent phenomena
We study how fluctuations in fluid dynamic fields can be dissipated or
amplified within the characteristic spatio-temporal structure of a heavy ion
collision. The initial conditions for a fluid dynamic evolution of heavy ion
collisions may contain significant fluctuations in all fluid dynamical fields,
including the velocity field and its vorticity components. We formulate and
analyze the theory of local fluctuations around average fluid fields described
by Bjorken's model. For conditions of laminar flow, when a linearized treatment
of the dynamic evolution applies, we discuss explicitly how fluctuations of
large wave number get dissipated while modes of sufficiently long wave-length
pass almost unattenuated or can even be amplified. In the opposite case of
large Reynold's numbers (which is inverse to viscosity), we establish that
(after suitable coordinate transformations) the dynamics is governed by an
evolution equation of non-relativistic Navier-Stokes type that becomes
essentially two-dimensional at late times. One can then use the theory of
Kolmogorov and Kraichnan for an explicit characterization of turbulent
phenomena in terms of the wave-mode dependence of correlations of fluid dynamic
fields. We note in particular that fluid dynamic correlations introduce
characteristic power-law dependences in two-particle correlation functions.Comment: 40 pages, 5 figures, published versio
Statistics of initial density perturbations in heavy ion collisions and their fluid dynamic response
Chapter 4: Heavy Ions at the Future Circular Collider
The Future Circular Collider (FCC) Study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadronâhadron collision mode, seven times larger than the nominal LHC energies. Operating such machine with heavy ions is an option that is being considered in the accelerator design studies. It would provide, for example, PbâPb and pâPb collisions at âsNN = 39 and 63 TeV, respectively, per nucleonânucleon collision, with integrated luminosities above 30 nbâ1 per month for PbâPb. This is a report by the working group on heavy-ion physics of the FCC Study. First ideas on the physics opportunities with heavy ions at the FCC are presented, covering the physics of the QuarkâGluon Plasma, of gluon saturation, of photon-induced collisions, as well as connections with other fields of high-energy physics
A next-generation LHC heavy-ion experiment
The present document discusses plans for a compact, next-generation multi-purpose detector at the LHC as a follow-up to the present ALICE experiment. The aim is to build a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X per layer, with the innermost layers possibly positioned inside the beam pipe. In addition to superior tracking and vertexing capabilities over a wide momentum range down to a few tens of MeV/, the detector will provide particle identification via time-of-flight determination with about 20~ps resolution. In addition, electron and photon identification will be performed in a separate shower detector. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector