# Subelliptic boundary value problems and The $G$-Fredholm Property

## TL;DR

This paper studies the $G$-Fredholm properties of the Laplacian on complex manifolds with boundary, showing finite $G$-dimension kernels and finite codimension images under group actions, extending classical elliptic theory to subelliptic settings.

## Contribution

It establishes that the Laplacian on certain complex manifolds with boundary has the $G$-Fredholm property, generalizing elliptic operator results to subelliptic and group-invariant contexts.

## Key findings

- The kernel of the Laplacian has finite $G$-dimension.
- The image of the Laplacian contains a closed, finite codimension, $G$-invariant subspace.
- Similar properties hold for the boundary Laplacian $ox_b$.

## Abstract

Let $G$ be a unimodular Lie group, $X$ a compact manifold with boundary, and $M$ be the total space of a principal bundle $G\to M\to X$ so that $M$ is also a complex manifold satisfying a local subelliptic estimate. In this work, we show that if $G$ acts by holomorphic transformations in $M$, then the Laplacian $\square=\bar\partial^{*}\bar\partial+\bar\partial\bar\partial^{*}$ on $M$ has the following properties: The kernel of $\square$ restricted to the forms $\Lambda^{p,q}$ with $q>0$ is a closed, $G$-invariant subspace in $L^{2}(M,\Lambda^{p,q})$ of finite $G$-dimension. Secondly, we show that if $q>0$, then the image of $\square$ contains a closed, $G$-invariant subspace of finite codimension in $L^{2}(M,\Lambda^{p,q})$. These two properties taken together amount to saying that $\square$ is a $G$-Fredholm operator. In similar circumstances, the boundary Laplacian $\square_b$ has similar properties.