Guido Gentile
Resummation of perturbation series and reducibility for Bryuno skew-product flows
(658K, postscript)

ABSTRACT.  We consider skew-product systems on ${\bf T}^d \times {\rm SL}(2,{\bf R})$ for Bryuno base flows close to constant coefficients, depending on a 
parameter, in any dimension $d$, and we prove reducibility for a large 
measure set of values of the parameter. The proof is based on a 
resummation procedure of the formal power series for the conjugation, 
and uses techniques of renormalisation group in quantum field theory.