Plane Curves Which are Quantum Homogeneous Spaces

Let C be a decomposable plane curve over an algebraically closed field k of characteristic 0. That is, C is defined in k(2) by an equation of the form g(x) = f (y), where g and f are polynomials of degree at least two. We use this data to construct three affine pointed Hopf algebras, A(x, a, g), A(y, b, f) and A(g, f), in the first two of which g [resp. f] are skew primitive central elements, with the third being a factor of the tensor product of the first two. We conjecture that A(g, f) contains the coordinate ring O(C) of C as a quantum homogeneous space, and prove this when each of g and f has degree at most five or is a power of the variable. We obtain many properties of these Hopf algebras, and show that, for small degrees, they are related to previously known algebras. For example, when g has degree three A(x, a, g) is a PBW deformation of the localisation at powers of a generator of the downup algebra A(-1,-1, 0). The final section of the paper lists some questions for future work.