An algebraic geometric model of an action of the face monoid associated to a Kac-Moody group on its building

TL;DR

This paper constructs an algebraic geometric model for the action of the face monoid associated with a Kac-Moody group on its building, extending previous work on monoid actions and spectrum descriptions.

Contribution

It provides an explicit algebraic geometric framework for the face monoid action on the building, including a detailed description of the spectrum of the Cartan algebra.

Findings

Full spectrum of homogeneous prime ideals of the Cartan algebra described

Established algebraic geometric model for face monoid action

Extended previous monoid action theories to a geometric setting

Abstract

The face monoid described in [M1] acts on the integrable highest weight modules of a symmetrizable Kac-Moody algebra. It has similar structural properties as a reductive algebraic monoid whose unit group is a Kac-Moody group. We found in [M5] two natural extensions of the action of the Kac-Moody group on its building to actions of the face monoid on the building. Now we give an algebraic geometric model of one of these actions of the face monoid. The building is obtained as a part of the spectrum of homogeneous prime ideals of the Cartan algebra of the Kac-Moody group. We describe the full spectrum of homogeneous prime ideals of the Cartan algebra.