Euclidean asymptotic expansions of Green functions of quantum fields (I)   Expansions of products of singular functions
  The problem of asymptotic expansions of Green functions in perturbative QFT is studied for the class of Euclidean asymptotic regimes. Phenomenological applications are analyzed to obtain a meaningful mathematical formulation of the problem. It is shown that the problem reduces to studying asymptotic expansions of products of a class of singular functions in the sense of the distribution theory. Existence, uniqueness and explicit expressions for such expansions ("asymptotic operation for products of singular functions") in dimensionally regularized form are obtained using the so-called extension principle. 
Fyodor V. Tkachov