7,065 research outputs found
QCD Dirac operator at nonzero chemical potential: lattice data and matrix model
Recently, a non-Hermitian chiral random matrix model was proposed to describe the eigenvalues
of the QCD Dirac operator at nonzero chemical potential. This matrix model can be constructed
from QCD by mapping it to an equivalent matrix model which has the same symmetries as QCD
with chemical potential. Its microscopic spectral correlations are conjectured to be identical to
those of the QCD Dirac operator. We investigate this conjecture by comparing large ensembles of
Dirac eigenvalues in quenched SU(3) lattice QCD at nonzero chemical potential to the analytical
predictions of the matrix model. Excellent agreement is found in the two regimes of weak and strong
non-Hermiticity, for several different lattice volumes
Adaptive Multigrid Algorithm for Lattice QCD
We present a new multigrid solver that is suitable for the Dirac operator in
the presence of disordered gauge fields. The key behind the success of the
algorithm is an adaptive projection onto the coarse grids that preserves the
near null space. The resulting algorithm has weak dependence on the gauge
coupling and exhibits very little critical slowing down in the chiral limit.
Results are presented for the Wilson Dirac operator of the 2d U(1) Schwinger
model.Comment: 4 pages, 2 figure
Chiral Symmetry Breaking and the Dirac Spectrum at Nonzero Chemical Potential
The relation between the spectral density of the QCD Dirac operator at
nonzero baryon chemical potential and the chiral condensate is investigated. We
use the analytical result for the eigenvalue density in the microscopic regime
which shows oscillations with a period that scales as 1/V and an amplitude that
diverges exponentially with the volume . We find that the discontinuity
of the chiral condensate is due to the whole oscillating region rather than to
an accumulation of eigenvalues at the origin. These results also extend beyond
the microscopic regime to chemical potentials .Comment: 4 pages, 1 figur
Unquenched complex Dirac spectra at nonzero chemical potential: Two-colour QCD lattice data versus matrix model
We compare analytic predictions of non-Hermitian chiral random matrix theory with the complex Dirac operator eigenvalue spectrum of two-color lattice gauge theory with dynamical fermions at nonzero chemical potential. The Dirac eigenvalues come in complex conjugate pairs, making the action of this theory real and positive for our choice of two staggered flavors. This enables us to use standard Monte Carlo simulations in testing the influence of the chemical potential and quark mass on complex eigenvalues close to the origin. We find excellent agreement between the analytic predictions and our data for two different volumes over a range of chemical potentials below the chiral phase transition. In particular, we detect the effect of unquenching when going to very small quark masses
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