Spectral measures associated to rank two Lie groups and finite subgroups of $GL(2,\mathbb{Z})$

Abstract

Spectral measures for fundamental representations of the rank two Lie groups $SU(3)$, $Sp(2)$ and $G_2$ have been studied. Since these groups have rank two, these spectral measures can be defined as measures over their maximal torus ${\mathbb{T}}^2$ and are invariant under an action of the corresponding Weyl group, which is a subgroup of $GL(2,\mathbb{Z})$. Here we consider spectral measures invariant under an action of the other finite subgroups of $GL(2,\mathbb{Z})$. These spectral measures are all associated with fundamental representations of other rank two Lie groups, namely ${\mathbb{T}}^2=U(1)\times U(1)$, $U(1)\times SU(2)$, $U(2)$, $SU(2)\times SU(2)$, $SO(4)$ and $PSU(3)$.

39 pages, 46 figures; new results added in Section 9, new Section 3.2, minor improvements to exposition throughout

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