The torus-knot slope-jump conjecture for the invariant Φ\Phi

Let Tn,n+1T_{n,n+1} denote the torus knot with parameters nn and n+1n+1, let ΦTn,n+1\Phi_{T_{n,n+1}} be the associated invariant, and write ΔΦTn,n+1(α)\Delta \Phi'_{T_{n,n+1}}(\alpha) for the jump in the slope of its function at α\alpha. Let s(Tn,n+1)s(T_{n,n+1}) denote the concordance invariant appearing in the statement. For other torus knots, use the notation ΦTp,q\Phi_{T_{p,q}} for the corresponding invariant.

Torus-knot slope-jump conjecture. For the torus knot Tn,n+1T_{n,n+1}, the jump in the slope ΔΦTn,n+1(α)\Delta \Phi'_{T_{n,n+1}}(\alpha) is equal to 00 except when α=2+2k2+3k\alpha=\frac{2+2k}{2+3k} for 0k<n0\leq k<n and kk has the same parity as nn, when it is 46k-4-6k. Together with

s(Tn,n+1)=n(n1),s(T_{n,n+1})=n(n-1),

this determines ΦTn,n1\Phi_{T_{n,n-1}}. For other torus knots, Φ\Phi is determined by the recurrence

ΦTp,q+p=ΦTp,q+ΦTp,p+1.\Phi_{T_{p,q+p}}=\Phi_{T_{p,q}}+\Phi_{T_{p,p+1}}.

The pattern is motivated by computations for small torus knots and would give the invariant Φ\Phi on the family of torus knots. The supplied text does not provide a resolution or further evidence beyond describing the pattern as a conjecture.

Sources & referencesView supporting material

Primary source

William Ballinger, “A family of concordance homomorphisms from Khovanov homology”, arXiv:2012.06030 (2020).

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