English

Lefschetz Theorem Using Real Morse Theory

Algebraic Geometry 2021-07-07 v2 Dynamical Systems

Abstract

We prove the Lefschetz hyperplane section theorem using a simpler machinery by making the observation that we can compose the Lefschetz Pencil with a Real Morse function to get a map from the variety to R\mathbb{R} which is "close" to being a Real Morse function. The proof uses a new method unlike the conventional one which uses vanishing cycles, thimbles and monodromy. We prove the genus formula for plane curves using Morse theory, Lefschetz pencil and B\'ezout's theorem. And then we prove the Riemann Hurwitz formula for ramified maps between curves by employing techniques from deformation theory. Lastly, we prove the Lefschetz Hyperplane Section Theorem solely using Real Morse Theory and exact sequences.

Keywords

Cite

@article{arxiv.2107.01591,
  title  = {Lefschetz Theorem Using Real Morse Theory},
  author = {Nima Rose Manjila and A. J. Parameswaran},
  journal= {arXiv preprint arXiv:2107.01591},
  year   = {2021}
}

Comments

16 pages, 1 figure

R2 v1 2026-06-24T03:52:29.751Z