Perturbative renormalisation of the Φ⁴4-ε model via generalised Wick maps

We consider the perturbative renormalisation of the Φ⁴d model from Euclidean quantum field theory for any possibly non-integer dimension d<4 . The so-called BPHZ renormalisation, named after Bogoliubov, Parasiuk, Hepp, and Zimmermann, is usually encoded into extraction-contraction operations on Feynman diagrams, which have a complicated combinatorics. We show that the same procedure can be encoded in the much simpler algebra of polynomials in two unknowns X and Y , which represent the fourth and second Wick power of the field. In this setting, renormalisation takes the form of a “Wick map” that maps monomials into Bell polynomials. The construction makes use of recent results by Bruned and Hou on multi-indices, which are algebraic objects of intermediate complexity between Feynman diagrams and polynomials.