Exotic holomorphic Engel structures on C4

Abstract

A holomorphic Engel structure determines a flag of distributions $\mathcal{W}\subset \mathcal{D}\subset \mathcal{E}$. We construct examples of Engel structures on ${\mathbf{C}}^4$ such that each of these distributions is hyperbolic in the sense that it has no tangent copies of $\mathbf{C}$. We also construct two infinite families of pairwise non-isomorphic Engel structures on ${\mathbf{C}}^4$ by controlling the curves $f:\mathbf{C}\to {\mathbf{C}}^4$ tangent to $\mathcal{W}$. The first is characterised by the topology of the set of points in ${\mathbf{C}}^4$ admitting $\mathcal{W}$-lines, and the second by a finer geometric property of this set. A consequence of the second construction is the existence of uncountably many non-isomorphic holomorphic Engel structures on ${\mathbf{C}}^4$.