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PGL2 skein algebras of small surfaces

Cole Ellison, Vijay Higgins, Mark Sandey, Eden Sylvester

math.GTarXiv:2610.01075

Abstract

We study the PGL2 skein algebras of small surfaces, focusing on the closed torus and the once-punctured torus. We provide explicit finite presentations by generators and relations for the PGL2 skein algebra of the torus and once-punctured torus, analogous to those of Bullock and Przytycki for the Kauffman bracket skein algebras. We give explicit bases of the PGL2 skein algebras of the torus and once-punctured torus and describe the multiplicative structure of the basis for the torus, analogous to the product-to-sum formula of Frohman and Gelca. We twist the basis for the torus to obtain one with structure constants in N[q,q-1]. We compute the kernels of natural maps between the PGL2 and Kauffman bracket skein algebras associated to the once-punctured torus and closed torus. We compute the center of the PGL2 skein algebra of the torus, which depends on the specialization of the quantum parameter q.

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