32 research outputs found
The Phase Diagram of 2 flavour QCD with improved Actions
It has been proposed, that the chiral continuum limit of 2-flavour QCD with
Wilson fermions is brought about by a phase in which flavour and parity
symmetry are broken spontaneously at finite lattice spacing. At finite
temperature this phase should retract from the weak coupling limit to form 5
cusps. This scenario is studied with tree level Symanzik improved actions for
both gauge and fermion fields on lattices of size and .Comment: Talk given at Conference on Strong and Electroweak Matter (SEWM 98),
Copenhagen, Denmark, 2-5 Dec 199
Two Flavour QCD Phase Transition
Results on the phase transition in QCD with two flavours of light staggered
fermions from an ongoing simulation are presented. We find the restoration of
the chiral SU(2) x SU(2) symmetry, but not of the axial U_A(1) symmetry.Comment: LaTeX2e, amstex package. 4 pages, 2 figures. Talk presented at the
10th International Conference on Problems of Quantum Field Theory, Crime
QCD thermodynamics from 3d adjoint Higgs model
The screening masses of hot SU(N) gauge theory, defined as poles of the
corresponding propagators are studied in 3d adjoint Higgs model, considered as
an effective theory of QCD, using coupled gap equations and lattice Monte-Carlo
simulations (for N=2). Using so-called lambda gauges non-perturbative evidence
for gauge independence of the pole masses within this class of gauges is given.
A possible application of the screening masses for the resummation of the free
energy is discussed.Comment: Talk given at the 5th International Workshop on Thermal Field Theory
and their Applications, Regensburg (Germany), August 1998, corrected typo
Towards the application of the Maximum Entropy Method to finite temperature Upsilon Spectroscopy
According to the Narnhofer Thirring Theorem interacting systems at finite
temperature cannot be described by particles with a sharp dispersion law. It is
therefore mandatory to develop new methods to extract particle masses at finite
temperature. The Maximum Entropy method offers a path to obtain the spectral
function of a particle correlation function directly. We have implemented the
method and tested it with zero temperature Upsilon correlation functions
obtained from an NRQCD simulation. Results for different smearing functions are
discussed.Comment: Lattice 2000 (Finite Temperature
Finite Temperature Phase Diagramm of QCD with improved Wilson fermions
We present first results of a study of two flavour QCD with Wilson fermions
at finite temperature. We have used tree level Symanzik improvement in both the
gauge and fermion part of the action. In a first step we explore the phase
diagramm on an lattice, with particular emphasis on checking
Aoki's conjecture with an improved action.Comment: Talk presented at LATTICE97(finite temperature), 3 pages, 3
Postscript figure
Numerical Study of Dense Adjoint Matter in Two Color QCD
We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential mu, for fermions in both fundamental and adjoint representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N=1 adjoint flavor on a 4^3x8 lattice are presented, using both hybrid Monte Carlo and Two-Step Multi-Boson algorithms. It is shown that the sign of the fermion determinant starts to fluctuate once the model enters a phase with non-zero baryon charge density. HMC simulations are not ergodic in this regime, but TSMB simulations retain ergodicity even in the dense phase, and in addition appear to show superior decorrelation. The HMC results for the equation of state and the pion mass show good quantitative agreement with the predictions of chiral perturbation theory, which should hold only for N>=2. The TSMB results incorporating the sign of the determinant support a delayed onset transition, consistent with the pattern of symmetry breaking expected for N=1
Cluster Percolation in O(n) Spin Models
The spontaneous symmetry breaking in the Ising model can be equivalently
described in terms of percolation of Wolff clusters. In O(n) spin models
similar clusters can be built in a general way, and they are currently used to
update these systems in Monte Carlo simulations. We show that for 3-dimensional
O(2), O(3) and O(4) such clusters are indeed the physical `islands' of the
systems, i.e., they percolate at the physical threshold and the percolation
exponents are in the universality class of the corresponding model. For O(2)
and O(3) the result is proven analytically, for O(4) we derived it by numerical
simulations.Comment: 11 pages, 8 figures, 2 tables, minor modification
Screening Masses of Hot SU(2) Gauge Theory from the 3D Adjoint Higgs Model
We study the Landau gauge propagators of the lattice SU(2) 3d adjoint Higgs
model, considered as an effective theory of high temperature 4d SU(2) gauge
theory. From the long distance behaviour of the propagators we extract the
screening masses. It is shown that the pole masses extracted from the
propagators agree well with the screening masses obtained recently in finite
temperature SU(2) theory. The relation of the propagator masses to the masses
extracted from gauge invariant correlators is also discussed. In so-called
lambda gauges non-perturbative evidence is given for the gauge independence of
pole masses within this class of gauges.Comment: Talk given at SEWM98 Conference, Copenhagen, December 199
Flow at the SPS and RHIC as a Quark Gluon Plasma Signature
Radial and elliptic flow in non-central heavy ion collisions can constrain
the effective Equation of State(EoS) of the excited nuclear matter. To this
end, a model combining relativistic hydrodynamics and a hadronic transport
code(RQMD [17]) is developed. For an EoS with a first order phase transition,
the model reproduces both the radial and elliptic flow data at the SPS. With
the EoS fixed from SPS data, we quantify predictions at RHIC where the Quark
Gluon Plasma(QGP) pressure is expected to drive additional radial and elliptic
flow. Currently, the strong elliptic flow observed in the first RHIC
measurements does not conclusively signal this nascent QGP pressure. Additional
measurements are suggested to pin down the EoS.Comment: 4 pages, 4 figures. Revised. Included discussed of v_2 (p_t) vs. b
and comparison to STAR dat
Application of the Maximum Entropy Method to the (2+1)d Four-Fermion Model
We investigate spectral functions extracted using the Maximum Entropy Method
from correlators measured in lattice simulations of the (2+1)-dimensional
four-fermion model. This model is particularly interesting because it has both
a chirally broken phase with a rich spectrum of mesonic bound states and a
symmetric phase where there are only resonances. In the broken phase we study
the elementary fermion, pion, sigma and massive pseudoscalar meson; our results
confirm the Goldstone nature of the pi and permit an estimate of the meson
binding energy. We have, however, seen no signal of sigma -> pi pi decay as the
chiral limit is approached. In the symmetric phase we observe a resonance of
non-zero width in qualitative agreement with analytic expectations; in addition
the ultra-violet behaviour of the spectral functions is consistent with the
large non-perturbative anomalous dimension for fermion composite operators
expected in this model.Comment: 25 pages, 13 figure