QUARK CONFINEMENT IN THE DECONFINED PHASE

In cylindrical volumes with C-periodic boundary conditions in the long direction, static quarks are confined even in the gluon plasma phase due to the presence of interfaces separating the three distinct high-t emperature phases. An effective ''string tension'' is computed analyti cally using a dilute gas of interfaces. At T-c, the deconfined-deconfi ned interfaces are completely wet by the confined phase and the high-t emperature ''string tension'' turns into the usual string tension belo w T-c. Finite size formulae are derived, which allow to extract interf ace and string tensions from the expectation value of a single Polyako v loop. A cluster algorithm is built for the 3-d three-state Potts mod el and an improved estimator for the Polyakov loop is constructed, bas ed on the number of clusters wrapping around the C-periodic direction of the cylinder.