Recursive Poincaré-polynomial conjecture for Khovanov homology of T(n,n)T(n,n)

Let Kn(t,q)K_n(t,q) denote the Poincaré polynomial of the Khovanov homology of T(n+1,n)T(n+1,n), and let Ln(t,q)L_n(t,q) denote that of T(n,n)T(n,n). Let Cn=1n+1(2nn)C_n=\frac{1}{n+1}\binom{2n}{n} be the nnth Catalan number. Recursive Poincaré-polynomial conjecture. The Poincaré polynomial LnL_n is recursively defined by

L0=1,L1=q1+q,L_0=1,\qquad L_1=q^{-1}+q,

and, for n2n\ge2,

Ln=t2n2(q6n8+q6n6)Ln2+i=1(n1)/2Ci1t2i(ni)q6i(ni)Ln2i+i=0(n2)/2((n2i)(n2i1))t2i(ni)q6i(ni)+n2i1Kn2i1.\begin{aligned} L_n={}&t^{2n-2}(q^{6n-8}+q^{6n-6})L_{n-2}+\sum_{i=1}^{\lfloor (n-1)/2\rfloor}C_{i-1}t^{2i(n-i)}q^{6i(n-i)}L_{n-2i}\\ &+\sum_{i=0}^{\lfloor (n-2)/2\rfloor}\left(\binom{n-2}{i}-\binom{n-2}{i-1}\right)t^{2i(n-i)}q^{6i(n-i)+n-2i-1}K_{n-2i-1}. \end{aligned}

This recurrence is presented as equivalent to the saddle-surjectivity conjecture and would determine the rational Khovanov homology of the torus links T(n,n)T(n,n) from the corresponding torus-knot polynomials.

Sources & referencesView supporting material

Primary source

Qiuyu Ren, “Lee filtration structure of torus links”, arXiv:2305.16089 (2024).

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