Reversible Skew Laurent Polynomial Rings and Deformations of Poisson Automorphisms

A skew Laurent polynomial ring S = R[x;α] is reversible if it has a reversing automorphism, that is, an automorphism θ of period 2 that transposes x and x and restricts to an automorphism γ of R with γ = γ. We study invariants for reversing automorphisms and apply our methods to determine the rings of invariants of reversing automorphisms of the two most familiar examples of simple skew Laurent polynomial rings, namely a localization of the enveloping algebra of the two-dimensional non-abelian solvable Lie algebra and the coordinate ring of the quantum torus, both of which are deformations of Poisson algebras over the base field F. Their reversing automorphisms are deformations of Poisson automorphisms of those Poisson algebras. In each case, the ring of invariants of the Poisson automorphism is the coordinate ring B of a surface in F and the ring of invariants S of the reversing automorphism is a deformation of B and is a factor of a deformation of F[x1, x2, x3] for a Poisson bracket determined by the appropriate surface.