Lorentz gauge and Gribov ambiguity in the compact lattice U(1) theory
The Gribov ambiguity problem is studied for compact U(1) lattice theory within the Lorentz gauge. In the Coulomb phase, it is shown that apart from double Dirac sheets all gauge (i.e. Gribov) copies originate mainly from the zero-momentum modes of the gauge fields. The removal of the zero–momentum modes turns out to be necessary for reaching the absolute maximum of the gauge functional F(θ) . A new gauge fixing procedure – zero-momentum Lorentz gauge – is proposed.
Dirac sheets and gauge fixing in U(1) lattice gauge theory
Abstract Photon correlators in U(1) pure gauge theory for different lattice actions are considered under the Lorentz gauge condition. They are shown to depend strongly on the gauge fixing ambiguity and on the corresponding existence of Dirac sheets. For the Coulomb phase a gauge fixing algorithm is proposed which avoids Dirac sheets and allows to find the global extremum of the non-local gauge condition.
Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems
We perform constant pressure Monte Carlo simulations of a spin-analogous model which describes coupled spatial and magnetic degrees of freedom on an fcc lattice. Our calculations qualitatively reproduce magnetovolume effects observed in some rare earth manganese compounds, especially in the anti-Invar material YMn2. These are a sudden collapse of the magnetic moment which is connected with a huge volume change, and a largely enhanced thermal expansion coefficient.