English

Real Zeuthen numbers for two lines

Algebraic Geometry 2007-10-08 v1

Abstract

Given three natural numbers k,l,dk,l,d such that k+l=d(d+3)/2k+l=d(d+3)/2, the Zeuthen number Nd(l)N_{d}(l) is the number of nonsingular complex algebraic curves of degree dd passing through kk points and tangent to ll lines in \PP2\PP^2. It does not depend on the generic configuration CC of points and lines chosen. If the points and lines are real, the corresponding number Nd\RR(l,C)N_{d}^\RR(l,C) of real curves usually depends on the configuration chosen. We use Mikhalkin's tropical correspondence theorem to prove that for two lines the real Zeuthen problem is maximal: there exists a configuration CC such that Nd\RR(2,C)=Nd(2)N_{d}^\RR(2,C)=N_{d}(2). The correspondence theorem reduces the computation to counting certain lattice paths with multiplicities.

Keywords

Cite

@article{arxiv.0710.1095,
  title  = {Real Zeuthen numbers for two lines},
  author = {Benoit Bertrand},
  journal= {arXiv preprint arXiv:0710.1095},
  year   = {2007}
}

Comments

6 pages, 3 figures

R2 v1 2026-06-21T09:27:00.271Z