Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit

Abstract

We present results for lattice QCD with staggered fermions in the limit of infinite gauge coupling, obtained from a worm-type Monte Carlo algorithm on a discrete spatial lattice but with continuous Euclidean time. This is achieved by sending both the anisotropy parameter $\gamma^2\simeq a/\at$ and the number of time-slices $N_\tau$ to infinity, keeping the ratio $\gamma^2/N_\tau \simeq aT$ fixed. In this limit, ambiguities arising from the anisotropy parameter $\gamma$ are eliminated and discretization errors usually introduced by a finite temporal lattice extent $\Nt$ are absent. The obvious gain is that no continuum extrapolation $N_\tau \rightarrow \infty$ has to be carried out. Moreover, the algorithm is faster and the sign problem disappears completely. As a first application, we determine the phase diagram as a function of temperature and real and imaginary baryon chemical potential. We compare our computations with those on lattices with discrete Euclidean time. Discretization errors due to finite $\Nt$ in previous studies turn out to be large at low temperatures.