The Hilbert space costratification for the orbit type strata of SU(2)-lattice gauge theory

TL;DR

This paper constructs a detailed quantum state space decomposition for SU(2) lattice gauge theory, linking classical gauge orbit structures to quantum operators using angular momentum theory and Wigner symbols.

Contribution

It introduces a novel method to explicitly determine the Hilbert space costratification for SU(2) lattice gauge theory, connecting classical stratification with quantum operator images via angular momentum combinatorics.

Findings

Explicit construction of the Hilbert space costratification for SU(2) gauge theory.

Development of an orthonormal basis and structure constants for the invariant function algebra.

Reduction of the Hamiltonian eigenvalue problem to linear algebra.

Abstract

We construct the Hilbert space costratification of $G=\mathrm{SU}(2)$-quantum gauge theory on a finite spatial lattice in the Hamiltonian approach. We build on previous work where we have implemented the classical gauge orbit strata on quantum level within a suitable holomorphic picture. In this picture, each element $\tau$ of the classical stratification corresponds to the zero locus of a finite subset $\{p_i\}$ of the algebra $\mathcal R$ of $G$-invariant representative functions on the complexification of $G^N$. Viewing the invariants as multiplication operators $\hat p_i$ on the Hilbert space $\mathcal H$, the union of their images defines a subspace of $\mathcal H$ whose orthogonal complement $\mathcal H_\tau$ is the element of the costratification corresponding to $\tau$. To construct $\mathcal H_\tau$, one has to determine the images of the $\hat p_i$ explicitly. To accomplish that goal, we construct an orthonormal basis in $\mathcal H$ and determine the multiplication law for the basis elements, that is, we determine the structure constants of $\mathcal R$ in this basis. This part of our analysis applies to any compact Lie group $G$. For $G = \mathrm{SU}(2)$, the above procedure boils down to a problem in combinatorics of angular momentum theory. Using this theory, we obtain the union of the images of the operators $\hat p_i$ as a subspace generated by vectors whose coefficients with respect to our basis are given in terms of Wigner's $3nj$ symbols. The latter are further expressed in terms of $9j$ symbols. Using these techniques, we are also able to reduce the eigenvalue problem for the Hamiltonian of this theory to a problem in linear algebra.