Generic properties of vector fields identical on a compact set and codimension one partially hyperbolic dynamics

Abstract: Let $\mathscr{X}^r(M)$ be the set of $C^r$ vector fields on a boundaryless compact Riemannian manifold $M$. Given a vector field $X_0\in\mathscr{X}^r(M)$ and a compact invariant set $\Gamma$ of $X_0$, we consider the closed subset $\mathscr{X}^r(M,\Gamma)$ of $\mathscr{X}^r(M)$, consisting of all $C^r$ vector fields which coincide with $X_0$ on $\Gamma$. Study of such a set naturally arises when one needs to perturb a system while keeping part of the dynamics untouched. A vector field $X\in\mathscr{X}^r(M,\Gamma)$ is called $\Gamma$-avoiding Kupka-Smale, if the dynamics away from $\Gamma$ is Kupka-Smale. We show that a generic vector field in $\mathscr{X}^r(M,\Gamma)$ is $\Gamma$-avoiding Kupka-Smale. In the $C^1$ topology, we obtain more generic properties for $\mathscr{X}^1(M,\Gamma)$. With these results, we further study codimension one partially hyperbolic dynamics for generic vector fields in $\mathscr{X}^1(M,\Gamma)$, giving a dichotomy of hyperbolicity and Newhouse phenomenon. As an application, we obtain that $C^1$ generically in $\mathscr{X}^1(M)$, a non-trivial Lyapunov stable chain recurrence class of a singularity which admits a codimension 2 partially hyperbolic splitting with respect to the tangent flow is a homoclinic class.