MOMENTUM EXPANSION OF 2-LOOP SELF-ENERGY DIAGRAMS IN THE STANDARD MODEL

We consider an algorithm for constructing the power series (in the ext ernal momentum) of two-loop two-point diagrams with arbitrary masses o f the internal particles. Comparison with a numerical calculation of s ome two-loop diagrams occurring in the Standard Model shows that the f irst few terms of the expansion provide good approximations in the reg ion when the external momentum is below the threshold.