Stefan Floerchinger

Fluctuations around Bjorken flow and the onset of turbulent phenomena

A bstractWe 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 Kol-mogorov 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.

Efimov effect from functional renormalization

We apply a field-theoretic functional renormalization-group technique to the few-body (vacuum) physics of nonrelativistic atoms near a Feshbach resonance. Three systems are considered: one-component bosons with a U(1) symmetry, two-component fermions with a

Large scale structure from viscous dark matter

\text{U}(1)\ifmmode\times\else\texttimes\fi{}\text{SU}(2)

Exact flow equation for composite operators

symmetry, and three-component fermions with a

Mode-by-mode fluid dynamics for relativistic heavy ion collisions

\text{U}(1)\ifmmode\times\else\texttimes\fi{}\text{SU}(3)

Modified Fermi-sphere, pairing gap and critical temperature for the BCS-BEC crossover

symmetry. We focus on the scale-invariant unitarity limit of an infinite scattering length. The exact solution for the two-body sector is consistent with the unitary fixed-point behavior of the considered systems. Nevertheless, the numerical three-body solution in the

How (non-)linear is the hydrodynamics of heavy ion collisions?

s

Chemical freeze-out in heavy ion collisions at large baryon densities

-wave sector develops a limit cycle scaling in case of U(1) bosons and SU(3) fermions. The Efimov parameter for the one-component bosons and the three-component fermions is found to be

Three-body loss in lithium from functional renormalization

s\ensuremath{\approx}1.006

Characterization of initial fluctuations for the hydrodynamical description of heavy ion collisions

, consistent with the result of Efimov.