Abstract:
We consider germs of $\mathcal{C}^{\infty}$ vector fields in $(\mathbb{R}^2, 0)$ with degenerate non-dicritic singularity (having ($n-1$)-jet zero and non-zero $n$-jet) and their corresponding foliations. Under some natural hypothesis we prove that the orbital formal equivalence of any two such vector fields implies their orbital $\mathcal{C}^{\infty}$ equivalence (and thus the $\mathcal{C}^{\infty}$ equivalence of the corresponding foliations). This result generalizes Chen Theorem for foliations defined by generic $\mathcal{C}^{\infty}$ germs of vector fields in $(\mathbb{R}^2, 0)$ having hyperbolic singularity.
Key words and phrases:formal normal forms, foliations, flat vector fields, rigidity.