Directed immersions for complex structures

Abstract

We analyze the differential relation corresponding to integrability of almost complex structures, reformulated as a directed immersion relation by Demailly and Gaussier. Combining results of Clemente [3], we show that applying h-principle techniques yields the following statement: for an almost complex manifold with arbitrary metric $(X,J,g)$, and for $\epsilon >0$, there exists a smooth function $f:X\to \mathbb{R}$ and almost complex structure $J^{\prime }$ on $X$ such that $J$ and $J^{\prime }$ are $C^0$-close on the graph of $f$ with respect to the extended metric on $X\times \mathbb{R}$, and such that the Nijenhuis tensor of $J^{\prime }$ on the graph has pointwise sup norm less than $C\epsilon$, where $C$ is a constant depending only on $J$ and $g$. This is an updated version of a previous preprint titled "Almost complex manifolds are (almost) complex".

This is an updated version of a previous preprint titled "Almost complex manifolds are (almost) complex"; most arguments are unchanged and the main theorem is restated correctly (that is, restated to what is actually proven by the arguments in the older version). Comments welcome