The deconfinement transition is studied close to the continuum limit of SO(3) lattice gauge theory. High barriers for tunnelling among different twist sectors causing loss of ergodicity for local update algorithms are circumvented by means of paralle
l tempering. We compute monopole and center vortex free energies both within the confining phase and through the deconfinement transition. We discuss in detail the general problem of defining order parameters for adjoint actions.
Maximal t Hooft loops are studied in SO(3) lattice gauge theory at finite temperature T. Tunneling barriers among twist sectors causing loss of ergodicity for local update algorithms are overcome through parallel tempering, enabling us to measure the
vortex free energy F and to identify a deconfinement transition at some $beta_A^{crit}$. The behavior of F below $beta_A^{crit}$ shows however striking differences with what is expected from discretizations in the fundamental representation.
In this letter we report on a numerical investigation of the Aoki phase in the case of finite temperature which continues our former study at zero temperature. We have performed simulations with Wilson fermions at $beta=4.6$ using lattices with tempo
ral extension $N_{tau}=4$. In contrast to the zero temperature case, the existence of an Aoki phase can be confirmed for a small range in $kappa$ at $beta=4.6$, however, shifted slightly to lower $kappa$. Despite fine-tuning $kappa$ we could not separate the thermal transition line from the Aoki phase.
We report on a numerical reinvestigation of the Aoki phase in lattice QCD with two flavors of Wilson fermions where the parity-flavor symmetry is spontaneously broken. For this purpose an explicitly symmetry-breaking source term $hbar{psi} i gamma_{5
} tau^{3}psi$ was added to the fermion action. The order parameter $<bar{psi} i gamma_{5}tau^{3}psi>$ was computed with the Hybrid Monte Carlo algorithm at several values of $(beta,kappa,h)$ on lattices of sizes $4^4$ to $12^4$ and extrapolated to $h=0$. The existence of a parity-flavor breaking phase can be confirmed at $beta=4.0$ and 4.3, while we do not find parity-flavor breaking at $beta=4.6$ and 5.0.
We report on a numerical reinvestigation of the Aoki phase in full lattice QCD with two flavors of unimproved Wilson fermions. For zero temperature the Aoki phase can be confirmed at inverse coupling $beta=4.0$ and $beta=4.3$, but not at $beta=4.6$ a
nd $beta=5.0$. At non-zero temperature the Aoki phase was found to exist also at $beta=4.6$.
We study the performance of QCD simulations with dynamical Wilson fermions by combining the Hybrid Monte Carlo algorithm with parallel tempering on $10^4$ and $12^4$ lattices. In order to compare tempered with standard simulations, covariance matrice
s between sub-ensembles have to be formulated and evaluated using the general properties of autocorrelations of the parallel tempering algorithm. We find that rendering the hopping parameter $kappa$ dynamical does not lead to an essential improvement. We point out possible reasons for this observation and discuss more suitable ways of applying parallel tempering to QCD.
The improvement of simulations of QCD with dynamical Wilson fermions by combining the Hybrid Monte Carlo algorithm with parallel tempering is studied on $10^4$ and $12^4$ lattices. As an indicator for decorrelation the topological charge is used.
In 4D compact U(1) lattice gauge theory with a monopole term added to the Wilson action we first reveal some properties of a third phase region at negative $beta$. Then at some larger values of the monopole coupling $lambda$ by a finite-size analysis
we find values of the critical exponent $ u$ close to, however, different from the Gaussian value.
We investigate four-dimensional compact U(1) lattice gauge theory with a monopole term added to the Wilson action. First we consider the phase structure at negative $beta$, revealing some properties of a third phase region there, in particular the ex
istence of a number of different states. Then our present studies concentrate on larger values of the monopole coupling $lambda$ where the confinement-Coulomb phase transition turns out to become of second order. Performing a finite-size analysis we find that the critical exponent $ u$ is close to, however, different from the gaussian value and that in the range considered $ u$ increases somewhat with $lambda$.
We investigate propagators in Lorentz (or Landau) gauge by Monte Carlo simulations. In order to be able to compare with perturbative calculations we use large $beta$ values. There the breaking of the Z(2) symmetry turns out to be important for all of
the four lattice directions. Therefore we make sure that the analysis is performed in the correct state. We discus implications of the gauge fixing mechanism and point out the form of the weak-coupling behavior to be expected in the presence of zero-momentum modes. Our numerical result is that the gluon propagator in the weak-coupling limit is strongly affected by zero-momentum modes. This is corroborated in detail by our quantitative comparison with analytical calculations.
