Background configurations, confinement and deconfinement on a lattice withBPS monopole boundary conditions

Finite temperature SU(2) lattice gauge theory is investigated in a three-di mensional cubic box with fixed boundary conditions provided by a discretize d, static Bogomol'nyi-Prasad-Sommerfield (BPS) monopole solution with varyi ng core scale mu. Using heating and cooling techniques, we establish that f or discrete mu-values stable classical solutions either of self-dual or of pure magnetic type exist inside the box. Having switched on quantum fluctua tions we compute the Polyakov line and other local operators. For different mu and at varying temperatures near the deconfinement transition we study the influence of the boundary condition on the vacuum inside the box. In co ntrast to the pure magnetic background field case, for the self-dual one we observe confinement even for temperatures quite far above the critical one .