CANCELLATION OF LADDER GRAPHS IN AN EFFECTIVE EXPANSION

A resummation of ladder graphs is important in cases where infrared, c ollinear, or light-cone singularities render the loop expansion invali d, especially at high temperature where these effects are often enhanc ed. It has been noted in some recent examples of this resummation that the ladder graphs are canceled by other types of terms. In this paper we show that this cancellation is quite general, and for the most par t algebraic. [S0556-2821(98)04504-4].