Structure of the gauge theory vacuum at finite temperatures

The space of moduli, i.e., the space of field configurations modulo gauge equivalence is constructed for calorons (self-dual gauge fields on ${\mathrm{R}}^3\times S^1$) with vanishing topological charge. Such calorons represent vacuum field configurations at a finite temperature. It is found that, unlike its zero-temperature counterpart, this space of moduli is nontrivial, being, in fact, a one-dimensional manifold.