English

On projections of smooth and nodal plane curves

Algebraic Geometry 2014-01-22 v3

Abstract

Suppose that CP2C\subset\mathbb P^2 is a general enough nodal plane curve of degree >2>2, ν ⁣:C^C\nu\colon \hat C\to C is its normalization, and π ⁣:C^P1\pi\colon \hat C\to\mathbb P^1 is a finite morphism simply ramified over the same set of points as a projection prpν ⁣:C^P1\mathrm{pr}_p\circ \nu\colon\hat C \to\mathbb P^1, where pP2Cp\in\mathbb P^2\setminus C (if degC=3\mathrm{deg}\, C=3, one should assume in addition that degπ4\deg\pi\ne4). We prove that the morphism π\pi is equivalent to such a projection if and only if it extends to a finite morphism X(P2)X\to(\mathbb P^2)^* ramified over CC^*, where XX is a smooth surface. As a by-product, we prove the Chisini conjecture for mappings ramified over duals to general nodal curves of any degree 3\ge3 except for duals to smooth cubics; this strengthens one of Victor Kulikov's results.

Keywords

Cite

@article{arxiv.1311.1904,
  title  = {On projections of smooth and nodal plane curves},
  author = {Yu. Burman and Serge Lvovski},
  journal= {arXiv preprint arXiv:1311.1904},
  year   = {2014}
}

Comments

Proofs simplified, a missing case supplied, and an important reference added