Polynomial algebras from Lie algebra reduction chains g ⊃ g'

Abstract

We reexamine different examples of reduction chains g ⊃ g′ of Lie algebras in order to show how the polynomials determining the commutant with respect to the subalgebra g′ leads to polynomial deformations of Lie algebras. These polynomial algebras have already been observed in various contexts, such as in the framework of superintegrable systems. Two relevant chains extensively studied in Nuclear Physics, namely the Elliott chain su(3) ⊃ so(3) and the chain so(5) ⊃ su(2) ×u(1) related to the Seniority model, are analysed in detail from this perspective. We show that these two chains both lead to three-generator cubic polynomial algebras, a result that paves the way for a more systematic investigation of nuclear models in relation to polynomial structures arising from reduction chains. In order to show that the procedure is not restricted to semisimple algebras, we also study the chain Ŝ(3) ⊃ sl(2, R) × so(2) involving the centrally-extended Schrödinger algebra in (3 + 1)-dimensional space–time. The approach chosen to construct these polynomial algebras is based on the use of the Lie-Poisson bracket, so that all the results are presented in the Poisson (commutative) setting. The advantage of considering this approach vs the enveloping algebras is emphasized, commenting on the main formal differences between the polynomial Poisson algebras and their noncommutative analogue. As an illustrative example of the latter, the three-generator cubic algebra associated to the Elliott chain is reformulated in the Lie algebraic (noncommutative) setting.