Large Mass Expansion versus Small Momentum Expansion of Feynman Diagrams

The method of the large mass expansion (LME) has the technical advantage that two-loop integrals occur only as bubbles with large masses. In many cases only one large mass occurs. In such cases these integrals are expressible in terms of Γfunctions, i.e. they can be handled completely analytically avoiding even recursions and therefore this approach may find a wide field of application. We consider it necessary to investigate the precision of this method and test it for several twoloop vertex functions ocurring in the Z → bb̄ decay by comparing it with the small momentum expansion. It turns out that in general high order approximants have to be taken into account for a sufficient accuracy. PACS numbers: 12.15.Ji; 12.15.Lk; 13.40.-b; 12.38.Bx; 11.10.Ji