Expected local topology of random complex submanifolds

Abstract

Let $n\geq 2$ and $r\in \{1, \cdots, n-1\}$ be integers, $M$ be a compact smooth K\''ahler manifold of complex dimension $n$, $E$ be a holomorphic vector bundle with complex rank $r$ and equipped with an hermitian metric $h_E$, and $L$ be an ample holomorphic line bundle over $M$ equipped with a metric $h$ with positive curvature form. For any $d\in \mathbb{N}$ large enough, we endorse the space of holomorphic sections $H^0(M,E\otimes L^d)$ with the natural Gaussian measure associated to $h_E$ , $h$ and its curvature form. Let $U\subset M$ be an open subset with smooth boundary. We prove that the average of the $(n-r)$-th Betti number of the vanishing locus in $U$ of a random section $s$ of $H^0(M,E\otimes L^d)$ is asymptotic to ${n-1 \choose r-1} d^n\int_U c_1(L)^n$ for large $d$. On the other hand, the average of the other Betti numbers are $o(d^n)$. The first asymptotic recovers the classical deterministic global algebraic computation. Moreover, such a discrepancy in the order of growth of these averages is new and constrasts with all known other smooth Gaussian models, in particular the real algebraic one. We prove a similar result for the affine complex Bargmann-Fock model.