Constraint Quantization of Slave-Particle Theories

We start from the Barnes-Coleman slave-particle description, where the Hubbard operators $X$ are decomposed into a product of fermionic ($f_{\alpha}$) and bosonic ($b$) operators. The quantum mechanical constraint $b^{\dagger} b + \sum_{\alpha} f_{\alpha}^{\dagger} f_{\alpha} = 1$ is treated within the framework of Dirac's method for the quantization of classical constrained systems. This leads to modified algebraic properties of the fundamental operators: $b b^{\dagger} b = b$, $f_{\alpha} f_{\beta}^{\dagger} f_{\gamma} = \delta_{\alpha \beta} f_{\gamma}$ and $f_{\alpha} b^{\dagger}= 0$. Thereby the algebra of the $X$-operators is preserved exactly on the operator level. Matrix representations of the above algebra are constructed and a resolvent-like perturbation theory for the single-impurity Anderson model is developed.