Deformation Openness of Big Fundamental Groups and Applications

TL;DR

This paper proves the deformation openness of big fundamental groups and related properties for smooth projective varieties, extending previous results and applying advanced techniques in complex geometry and harmonic maps.

Contribution

It establishes the deformation invariance of big fundamental groups for varieties with big local systems and addresses conjectures by Campana and Claudon.

Findings

Proves deformation openness of big fundamental groups for certain varieties.

Develops deformation regularity of equivariant pluriharmonic maps.

Applies results to pseudo-Brody hyperbolicity and related conjectures.

Abstract

In 2001, de Oliveira, Katzarkov, and Ramachandran conjectured that the property of smooth projective varieties having big fundamental groups is stable under small deformations. This conjecture was proven by Beno\^it Claudon in 2010 for surfaces and for threefolds under suitable assumptions. In this paper, we prove this conjecture for smooth projective varieties admitting a big complex local system. Moreover, we address a more general conjecture by Campana and Claudon concerning the deformation invariance of the \(\Gamma\)-dimension of projective varieties. As an application, we establish the deformation openness of pseudo-Brody hyperbolicity for projective varieties endowed with a big and semisimple complex local system. To achieve these results, we develop the deformation regularity of equivariant pluriharmonic maps into Euclidean buildings and Riemannian symmetric spaces in families, along with techniques from the reductive and linear Shafarevich conjectures.