The Alexander polynomial coefficient inequality for rational cuspidal curves

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Let CC be a rational cuspidal curve of degree dd with critical points z1,…,znz_1,\ldots,z_n. Let K1,…,KnK_1,\ldots,K_n be the corresponding links of singular points, with Alexander polynomials Δ1,…,Δn\Delta_1,\ldots,\Delta_n, and let G1,…,GnG_1,\ldots,G_n be their gap sequences. Set

g=∣G1∣+∣G2∣+…+∣Gn∣g=|G_1|+|G_2|+\ldots+|G_n|

so that gg is the genus of KK. Write

Δ(t)=1+(t−1)g+(t−1)2∑j=02g−2kl\Delta(t)=1+(t-1)g+(t-1)^2\sum_{j=0}^{2g-2}k_l

and let I=I1⋄I2⋄…⋄InI=I_1\diamond I_2\diamond\ldots\diamond I_n. The Alexander polynomial coefficient inequality. For every j=0,…,d−3j=0,\ldots,d-3,

kd(d−j−3)≤I(d(d−j−3)+1),k_{d(d-j-3)}\leq I\bigl(d(d-j-3)+1\bigr),

with equality for n=1n=1. This conjecture concerns restrictions on the Alexander polynomials and gap sequences of rational cuspidal curves; the equality case for one critical point was verified by Borodzik and Livingston, while the general case remains open in the supplied source.

References

Primary source

Piotr Nayar and Barbara Pilat, “A note on the rational cuspidal curves”, arXiv:1406.3104 (2014).

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