December 3, 2007
15h15: *Feynman-like combinatorial diagrams and the EGF Hadamard Product*
By G.H.E.Duchamp (LIPN, Université Paris XIII)

**Abstract.** We consider two aspects of the
product formula for formal power series applied to combinatorial field
theories. Firstly, we remark that the case when the functions involved
in the product formula are free exponentials (like in the derivation
of Bell polynomials) is of special interest as it leads to groups of
substitutions and a correspondence with vector fields on the
line. Secondly, we discuss deformations (counting natural graph
parameters as crossings and superpositions) of the Feynman-like
algebra arising from the product formula of two free
exponentials. This results in a true Hopf deformation of this algebra.

Contact Information Virginie Collette