Ordnungen des Sehens / Systems of Perception
Towards corrections to the strong coupling limit of staggered lattice QCD : the XXIX International Symposium on Lattice Field Theory - Lattice 2011, July 10 - 16, 2011, Squaw Valley, Lake Tahoe, California
Philippe de Forcrand
- We report on the first steps of an ongoing project to add gauge observables and gauge corrections
to the well-studied strong coupling limit of staggered lattice QCD, which has been shown earlier
to be amenable to numerical simulations by the worm algorithm in the chiral limit and at finite
density. Here we show how to evaluate the expectation value of the Polyakov loop in the framework
of the strong coupling limit at finite temperature, allowing to study confinement properties
along with those of chiral symmetry breaking. We find the Polyakov loop to rise smoothly, thus
signalling deconfinement. The non-analytic nature of the chiral phase transition is reflected in the
derivative of the Polyakov loop. We also discuss how to construct an effective theory for non-zero
lattice coupling, which is valid to O(b).
Implications on the collision dynamics via azimuthal sensitive HBT from UrQMD : the Seventh Workshop on Particle Correlations and Femtoscopy, September 20 - 24 2011, University of Tokyo, Japan
Michael Annan Lisa
- We explore the shape and orientation of the freezeout region of non-central heavy ion collisions.
For this we fit the freezeout distribution with a tilted ellipsoid. The resulting tilt angle is compared
to the same tilt angle extracted via an azimuthally sensitive HBT analysis. This allows to access
the tilt angle experimentally, which is not possible directly from the freezeout distribution. We
also show a systematic study on the system decoupling time dependence on dNch/dh, using HBT
results from the UrQMD transport model. In this study we found that the decoupling time scales
with (dNch/dh)1/3 within each energy, but the scaling is broken across energies.
Effective theory for QCD at finite temperature and density from strong coupling expansion
- QCD at finite temperature and denisty remains intractable by Monte Carlo simulations for quark
chemical potentials m >∼T. It has been a long standing problem to derive effective theories from
QCD which describe the phase structure of the former with controlled errors. We propose a
solution to this problem by a combination of analytical and numerical methods. Starting from
lattice QCD with in Wilson’s formulation, we derive an effective action in terms of Polyakov
loops by means of combined strong coupling and hopping expansions. The theory correctly
reflects the centre-symmetry in the pure gauge limit and its breaking through quarks. It is valid
for heavy quarks and lattices up to Nt ∼ 6. Its sign problem can be solved and we are able to
calculate the deconfinement transition of QCD with heavy quarks for all chemical potentials.
Strong coupling effective theory with heavy fermions
- We extend the recently developed strong coupling, dimensionally reduced Polyakov-loop effective
theory from finite-temperature pure Yang-Mills to include heavy fermions and nonzero chemical
potential by means of a hopping parameter expansion. Numerical simulation is employed to
investigate the weakening of the deconfinement transition as a function of the quark mass. The
tractability of the sign problem in this model is exploited to locate the critical surface in the
(M/T,m/T,T) space over the whole range of chemical potentials from zero up to infinity.
Hagedorn states and thermalization : XLIX International Winter Meeting on Nuclear Physics, 24 - 28 January 2011, Bormio, Italy
- In recent years, Hagedorn states have been used to explain the equilibrium and transport properties of a hadron gas close to the QCD critical temperature. These massive resonances are shown to lower h/s to near the AdS/CFT limit close to the phase transition. A comparison of the Hagedorn model to recent lattice results is made and it is found that the hadrons can reach chemical equilibrium almost immediately, well before the chemical freeze-out temperatures found in thermal fits for a hadron gas without Hagedorn states.
LatticeQCD using OpenCL
- We report on our implementation of LatticeQCD applications using OpenCL. We focus on the
general concept and on distributing different parts on hybrid systems, consisting of both CPUs
(Central Processing Units) and GPUs (Graphic Processing Units).
Constraints on the two-flavor QCD phase diagram from imaginary chemical potential : the XXIX International Symposium on Lattice Field Theory - Lattice 2011, July 10 - 16, 2011, Squaw Valley, Lake Tahoe, California
Philippe de Forcrand
- We review our knowledge of the phase diagram of QCD as a function of temperature, chemical
potential and quark masses. The presence of tricritical lines at imaginary chemical potential
m = i p 3 T, with known scaling behaviour in their vicinity, puts constraints on this phase diagram,
especially in the case of two light flavors. We show first results in our project to determine the
finite-temperature behaviour in the Nf = 2 chiral limit.
On the universal critical behavior in 3-flavor QCD
- We analyze the universal critical behavior at the chiral critical point in QCD with three degenerate
quark masses. We confirm that this critical point lies in the universality class of the three
dimensional Ising model. The symmetry of the Ising model, which is Z(2), is not directly realized
in the QCD Hamiltonian. After making an ansatz for the magnetization- and energy-like operators
as linear admixtures of the chiral condensate and the gluonic action, we determine several
non-universal mixing and normalization constants. These parameters determine an unambiguous
mapping of the critical behavior in QCD to that of the 3d-Ising model. We verify its validity by
showing that the thus obtained orderparameter scales in accordance with the magnetic equation
of state of the 3d-Ising model.
Microscopic Calculation of Heavy-Ion Potentials Based on TDHF
A. Sait Umar
Joachim A. Maruhn
- We discuss the implementation and results of a recently developed microscopic method for calculating ion-ion interaction potentials and fusion cross-sections. The method uses the TDHF evolution to obtain the instantaneous many-body collective state using a density constraint. The ion-ion potential as well as the coordinate dependent mass are calculated from these states. The method fully accounts for the dynamical processes present in the TDHF time-evolution and provides a parameter-free way of calculating fusion cross-sections.