Characterizing slopes for torus knots

Abstract

A slope $\frac pq$ is called a characterizing slope for a given knot $K_0$ in $S^3$ if whenever the $\frac pq$-surgery on a knot $K$ in $S^3$ is homeomorphic to the $\frac pq$-surgery on $K_0$ via an orientation preserving homeomorphism, then $K=K_0$. In this paper we try to find characterizing slopes for torus knots $T_{r,s}$. We show that any slope $\frac pq$ which is larger than the number $\frac{30(r^2-1)(s^2-1)}{67}$ is a characterizing slope for $T_{r,s}$. The proof uses Heegaard Floer homology and Agol--Lackenby's 6--Theorem. In the case of $T_{5,2}$, we obtain more specific information about its set of characterizing slopes by applying more Heegaard Floer homology techniques.Comment: Version 2: 19 pages. This is a major revision. The title of the first version was "Towards a Dehn surgery characterization of $T_{5,2}$". We extended the result in the first version to general torus knots. We also fixed a gap in the first version, so our result for $T_{5,2}$ is slightly weaker than the originally claimed on