ON THE INFINITE-ORDER RESUMATION OF SOME FINITE-TEMPERATURE DIAGRAMS

In the scalar phi4 theory we discuss the behavior of the thermal four- point amplitude, after making a resumation of an infinite chain of loo ps. The calculation is presented in the thermofield dynamics formalism . It is shown that the zero temperature contribution to the real part of the amplitude has no differences with respect to the usual one-loop result. This is not the case, however, for the temperature-dependent part, where the loop resumation implies a completely different behavio r of the amplitude, for the real as well as for the imaginary parts, c ompared to the one-loop result.