On the Complement of the Dense Orbit for a Quiver of Type 𝔸

Abstract

Let 𝔸 _t be the directed quiver of type 𝔸 with t vertices. For each dimension vector d, there is a dense orbit in the corresponding representation space. The principal aim of this note is to use just rank conditions to define the irreducible components in the complement of the dense orbit. Then we compare this result with already existing ones by Knight and Zelevinsky, and by Ringel. Moreover, we compare with the fan associated to the quiver 𝔸 _t and derive a new formula for the number of orbits using nilpotent classes. In the complement of the dense orbit, we determine the irreducible components and their codimension. Finally, we consider several particular examples.

Key Words:

• Dense orbit
• Irreducible component
• Multi segment
• Quiver

2010 Mathematics Subject Classification:

• 16G20
• 14L35
• 20G05

ACKNOWLEDGMENT

This work started during a stay of both authors in Oberwolfach. We are indebted to the Institut for the perfect working conditions. The second author was supported by the DFG priority program SPP 1388 representation theory.

Notes

Communicated by D. Zacharia.