The topological aspect of the holonomy displacement on the principal $U(n)$ bundles over Grassmanian manifolds

TL;DR

This paper explores the topological properties of holonomy displacement in principal $U(n)$ bundles over Grassmannian manifolds, linking geometric areas with holonomy angles in a precise mathematical framework.

Contribution

It characterizes the holonomy displacement on these bundles in terms of the area enclosed by curves on totally geodesic surfaces, revealing a topological aspect of the holonomy in complex Grassmannian geometry.

Findings

Holonomy displacement relates to the area enclosed by curves on geodesic surfaces.

Holonomy is trivial (identity) when the bundle is flat.

The holonomy angle is proportional to the surface area, with a specific coefficient.

Abstract

Consider the principal $U(n)$ bundles over Grassmann manifolds $U(n)\rightarrow U(n+m)/U(m) \stackrel{\pi}\rightarrow G_{n,m}$. Given $X \in U_{m,n}(\mathbb{C})$ and a 2-dimensional subspace $\mathfrak{m}' \subset \mathfrak{m} $ $ \subset \mathfrak{u}(m+n), $ assume either $\mathfrak{m}'$ is induced by $X,Y \in U_{m,n}(\mathbb{C})$ with $X^{*}Y = \mu I_n$ for some $\mu \in \mathbb{R}$ or by $X,iX \in U_{m,n}(\mathbb{C})$. Then $\mathfrak{m}'$ gives rise to a complete totally geodesic surface $S$ in the base space. Furthermore, let $\gamma$ be a piecewise smooth, simple closed curve on $S$ parametrized by $0\leq t\leq 1$, and $\widetilde{\gamma}$ its horizontal lift on the bundle $U(n) \rightarrow \pi^{-1}(S) \stackrel{\pi}{\rightarrow} S,$ which is immersed in $U(n) \rightarrow U(n+m)/U(m) \stackrel{\pi}\rightarrow G_{n,m} $. Then $$ \widetilde{\gamma}(1)= \widetilde{\gamma}(0) \cdot ( e^{i \theta} I_n) \quad \text{ or } \quad \widetilde{\gamma}(1)= \widetilde{\gamma}(0), $$ depending on whether the immersed bundle is flat or not, where $A(\gamma)$ is the area of the region on the surface $S$ surrounded by $\gamma$ and $\theta= 2 \cdot \tfrac{n+m}{2n} A(\gamma).$