A resummed perturbative expansion is used to obtain the self-energy in the high-temperature $g^2{\phi }^4$ field-theory model up to order $g^4$. From this the zero-momentum pole of the effective propagator is evaluated to determine the induced thermal mass and damping rate for the bosons in the plasma to order $g^3$. The calculations are performed in the imaginary-time formalism and a simple diagrammatic analysis is used to identify the relevant diagrams at each order. Results are compared with similar real-time calculations found in the literature.

• Received 13 January 1992

DOI:https://doi.org/10.1103/PhysRevD.45.4695