Parametrizing spaces of positive representations

TL;DR

This paper explores parametrizations of spaces of positive framed representations of surface groups into semisimple Lie groups, analyzing their topology, homotopy type, and connected components, extending Lusztig's total positivity concepts.

Contribution

It provides new parametrizations and topological descriptions of positive representation spaces for general semisimple Lie groups, generalizing previous Lusztig-based frameworks.

Findings

Number of connected components matches that of positive representations.

Explicit parametrizations of positive framed representation spaces.

Determined the connected components for simple Lie groups.

Abstract

Using Lusztig's total positivity in split real Lie groups V. Fock and A. Goncharov have introduced spaces of positive (framed) representations. For general semisimple Lie groups a generalization of Lusztig's total positivity was recently introduced by O. Guichard and A. Wienhard. They also introduced the associated space of positive representations. Here we consider the corresponding spaces of positive framed representations of the fundamental group of a punctured surface. We give several parametrizations of the spaces of framed positive representations. Using these parametrizations, we describe their topology and their homotopy type. We show that the number of connected components of the space of framed positive representations agrees with the number of connected components of the space of positive representations, and determine this number for simple Lie groups. Along the way, we also parametrize, for an arbitrary semisimple Lie group, the space of representations of the fundamental group of a punctured surface which are transverse with respect to a fixed ideal triangulation of the surface.