58 research outputs found
Two-colour Lattice QCD with dynamical fermions at non-zero density versus Matrix Models
We provide first evidence that Matrix Models describe the low lying complex
Dirac eigenvalues in a theory with dynamical fermions at non-zero density.
Lattice data for gauge group SU(2) with staggered fermions are compared to
detailed analytical results from Matrix Models in the corresponding symmetry
class, the complex chiral Symplectic Ensemble. They confirm the predicted
dependence on chemical potential, quark mass and volume.Comment: 6 pages, 8 fig., talk given at Lattice 2005 (Finite Temperature and
Density) Dublin and Extreme QCD Swanse
Quantum chaos in supersymmetric QCD at finite density
We investigate the distribution of the spacings of adjacent eigenvalues of
the lattice Dirac operator. At zero chemical potential , the
nearest-neighbor spacing distribution follows the Wigner surmise of
random matrix theory both in the confinement and in the deconfinement phase.
This is indicative of quantum chaos. At nonzero chemical potential, the
eigenvalues of the Dirac operator become complex and we discuss how can
be defined in the complex plane. Numerical results from an SU(2) simulation
with staggered fermions in fundamental and adjoint representations are compared
with predictions from non-hermitian random matrix theory, and agreement with
the Ginibre ensemble is found for .Comment: Contribution to the Workshop on ``Finite Density QCD'' (Nara, Japan,
2003-07-10 -- 2003-07-12); 6 pages, 12 figure
Parallel-tempering cluster algorithm for computer simulations of critical phenomena
In finite-size scaling analyses of Monte Carlo simulations of second-order
phase transitions one often needs an extended temperature range around the
critical point. By combining the parallel tempering algorithm with cluster
updates and an adaptive routine to find the temperature window of interest, we
introduce a flexible and powerful method for systematic investigations of
critical phenomena. As a result, we gain one to two orders of magnitude in the
performance for 2D and 3D Ising models in comparison with the recently proposed
Wang-Landau recursion for cluster algorithms based on the multibondic
algorithm, which is already a great improvement over the standard
multicanonical variant.Comment: pages, 5 figures, and 2 table
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
Density profiles of small Dirac operator eigenvalues for two color QCD at nonzero chemical potential compared to matrix models
We investigate the eigenvalue spectrum of the stagerred Dirac matrix in two color QCD at finite chemical potential. The profiles of complex eigenvalues close to the origin are compared to a complex generalization of the chiral Gaussian Symplectic Ensemble, confirming its predictions for weak and strong non-Hermiticity. They differ from the QCD symmetry class with three colors by a level repulsion from both the real and imaginary axis
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