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 Gamma-functions, 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 two-loop vertex functions ocurring in the Z --> <b(b)over bar> decay by comparing it with the small momentum expansion. It turns out that in general high order approximants have ro be taken into account for a sufficient accuracy. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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