  We impose the periodicity conditions corresponding to the Matsubara formalism
for Thermal Field Theory as constraints in the imaginary time path integral.
These constraints are introduced by means of time-independent auxiliary fields
which, by integration of the original variables, become dynamical fields in the
resulting `dual' representation for the theory. This alternative representation
has the appealing property of involving fields which live in one dimension less
than the original ones, with a quantum partition function whose integration
measure is identical to the one of its classical counterpart, albeit with a
different (spatially nonlocal) action.
