  Nonperturbative infrared finite solutions for the gluon polarization tensor
have been found, and the possibility that gluons may have a dynamically
generated mass is supported by recent Monte Carlo simulation on the lattice.
These solutions differ among themselves, due to different approximations
performed when solving the Schwinger-Dyson equations for the gluon polarization
tensor. Only approximations that minimize energy are meaningful, and, according
to this, we compute an effective potential for composite operators as a
function of these solutions in order to distinguish which one is selected by
the vacuum.
