Preprint D3/2004
Non-Periodic Bifurcations of One-Dimensional Maps

Paulo RogĂ©rio Sabini

**Keywords: **
Non-periodic bifurcations | non-uniform hyperbolicity

We prove that a 'positive probability' subset of the boundary of '{uniformly expanding circle transformations}' consists of Kupka-Smale maps. More precisely, we construct an open class of $2$-parameter families of circle maps $(f_{a,\theta})_{a,\theta}$ such that for a positive Lebesgue measure subset of values of $a$, the family $(f_{a,\theta})_\theta$ leaves the uniformly expanding domain at a
map for which all periodic points are hyperbolic (expanding) and
no critical point is pre-periodic. Furthermore, these maps admit an absolutely continuous invariant measure. We also provide information about the geometry of the boundary of the set of hyperbolic maps.