One-particle-irreducible amputated graphs differ qualitatively at finite temperature when calculated in the imaginary-time and real-time formalisms. Here we show within the real-time formalism for the three-point function that when external propagators are attached certain amputated functions can be inferred which have a close relation to those of the imaginary-time formalism.

• Received 16 May 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1384