# The second fundamental form of the real Kaehler submanifolds

## TL;DR

This paper investigates the second fundamental form of real Kaehler submanifolds in Euclidean space, providing evidence supporting a conjecture about their geometric structure in low codimension cases.

## Contribution

It proves that the second fundamental form behaves as predicted by the conjecture for low codimension, advancing understanding of Kaehler submanifold geometry.

## Key findings

- Second fundamental form aligns with conjectured behavior in low codimension cases
- Supports the conjecture for codimension up to 11
- Counterexample indicates limitations for higher codimension

## Abstract

Let $f\colon M^{2n}\to\R^{2n+p}$, $2\leq p\leq n-1$, be an isometric immersion of a Kaehler manifold into Euclidean space. Yan and Zheng conjectured in \cite{YZ} that if the codimension is $p\leq 11$ then, along any connected component of an open dense subset of $M^{2n}$, the submanifold is as follows: it is either foliated by holomorphic submanifolds of dimension at least $2n-2p$ with tangent spaces in the kernel of the second fundamental form whose images are open subsets of affine vector subspaces, or it is embedded holomorphically in a Kaehler submanifold of $\R^{2n+p}$ of larger dimension than $2n$. This bold conjecture was proved by Dajczer and Gromoll just for codimension three and then by Yan and Zheng for codimension four. In this paper we prove that the second fundamental form of the submanifold behaves pointwise as expected in case that the conjecture is true. This result is a first fundamental step for a possible classification of the non-holomorphic Kaehler submanifolds lying with low codimension in Euclidean space. A counterexample shows that our proof does not work for higher codimension, indicating that proposing $p=11$ in the conjecture as the largest codimension is appropriate.