TOPOLOGICAL STEPS TOWARD THE HOMFLYPT SKEIN MODULE OF THE LENS SPACES L(p, 1) VIA BRAIDS

In this paper we work toward the Homflypt skein module of the lens spaces L(p, 1), S(L(p, 1)), using braids. In particular, we establish the connection between S(ST), the Homflypt skein module of the solid torus ST, and S(L(p, 1)) and arrive at an infinite system, whose solution corresponds to the computation of S(L(p,1)). We start from the Lambropoulou invariant X for knots and links in ST, the universal analogue of the Homflypt polynomial in ST, and a new basis, Λ, of S(ST) presented in [DL1]. We show that S(L(p, 1)) is obtained from S(ST) by considering relations coming from the performance of braid band moves (bbm) on elements in the basis Λ, where the braid band moves are performed on any moving strand of each element in Λ. We do that by proving that the system of equations obtained from diagrams in ST by performing bbm on any moving strand is equivalent to the system obtained if we only consider elements in the basic set Λ. The importance of our approach is that it can shed light to the problem of computing skein modules of arbitrary c.c.o. 3-manifolds, since any 3-manifold can be obtained by surgery on S along unknotted closed curves. The main difficulty of the problem lies in selecting from the infinitum of band moves some basic ones and solving the infinite system of equations. 0. Introduction In this paper we relate the Homflypt skein module of the lens spaces L(p, 1), S(L(p, 1)), to the Homflypt skein module of the solid torus, S(ST). This work is part of the PhD thesis of the first author [D] and in [DL3] we develop an algebraic approach to the computation of the Homflypt skein module of the lens space L(p, 1) via braids. Skein modules are quotients of free modules over ambient isotopy classes of knots and links in a 3-manifold by properly chosen skein relations. The skein module of a 3-manifold M based on the Homflypt skein relation is called the Homflypt skein module of M , also known as Conway skein module and as 3 skein module ([P, P2]). More precisely, let M be an oriented 3-manifold, R = Z[u±1, z±1], L the set of all ambient isotopy classes of oriented links in M and let S the submodule of RL generated by the skein expressions uL+ − uL− − zL0, where L+, L− and L0 comprise a Conway triple represented schematically by the illustrations in Figure 1. 2010 Mathematics Subject Classification. 57M27, 57M25, 57Q45, 20F36, 20C08.