Local intersection multiplicity conjecture for cuspidal curves and their 2-Hessians

Let CC be a cuspidal plane algebraic curve and let H2H_2 be its 2-Hessian curve. At a point pCp\in C, write mm for the multiplicity of CC at pp, δ\delta for its delta invariant, ll for the intersection multiplicity of CC with its tangent at pp, and cc for its intersection multiplicity with an osculating conic at pp. Local intersection multiplicity conjecture. The intersection multiplicity (H2C)p(H_2\cdot C)_p is determined as follows. If l2ml\neq 2m, then

(H2C)p=24δ+3m+3l12.(H_2\cdot C)_p=24\delta+3m+3l-12.

If l=2ml=2m, then

(H2C)p=24δ+7m+c12.(H_2\cdot C)_p=24\delta+7m+c-12.

The conjecture gives a local geometric interpretation of the correction terms in the global Bézout formula for the intersection of a cuspidal curve with its 2-Hessian. It was verified for all rational cuspidal curves of degrees 44 and 55; the corresponding analogous result for Hessian curves is known, while the general case remains open.

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Primary source

Paul Aleksander Maugesten and Torgunn Karoline Moe, “The 2-Hessian and sextactic points on plane algebraic curves”, arXiv:1709.01698 (2018).

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