Nilpotent structures of oriented neutral vector bundles

In this paper, we study nilpotent structures of an oriented vector bundle $E$ of rank $4n$ with a neutral metric $h$ and an $h$-connection $\nabla$. We define $H$-nilpotent structures of $(E, h, \nabla )$ for a Lie subgroup $H$ of $SO(2n, 2n)$ related to neutral hyperK\"{a}hler structures. We observe that there exist a complex structure $I$ and paracomplex structures $J_1$, $J_2$ of $E$ such that $h$, $\nabla$, $I$, $J_1$, $J_2$ form a neutral hyperK\"{a}hler structure of $E$ if and only if there exists an $H$-nilpotent structure of $(E, h, \nabla )$.