English

Critical points of modular forms

Number Theory 2024-07-16 v2

Abstract

We count the number of critical points of a modular form with real Fourier coefficients in a γ\gamma-translate of the standard fundamental domain F\mathcal{F} (with γSL2(Z)\gamma\in \mathrm{SL}_2(\mathbb{Z})). Whereas by the valence formula the (weighted) number of zeros of this modular form in γF\gamma\mathcal{F} is a constant only depending on its weight, we give a closed formula for this number of critical points in terms of those zeros of the modular form lying on the boundary of F,\mathcal{F}, the value of γ1()\gamma^{-1}(\infty) and the weight. More generally, we indicate what can be said about the number of zeros of a quasimodular form.

Keywords

Cite

@article{arxiv.2204.00432,
  title  = {Critical points of modular forms},
  author = {Jan-Willem van Ittersum and Berend Ringeling},
  journal= {arXiv preprint arXiv:2204.00432},
  year   = {2024}
}

Comments

27 pages; final version with minor changes

R2 v1 2026-06-24T10:34:41.308Z