Calculation of finite-temperature effects in field theories

We discuss an alternative method for computing finite-temperature effects in field theories, within the framework of the imaginary-time formalism. Our approach allows for a systematic calculation of the high-temperature expansion in terms of Riemann $\zeta$ functions. The imaginary-time result is analyically continued to the complex plane. We are able to obtain the real-time limit of the real and the imaginary parts of the Green's functions.