English

Numerical spectrums control Cohomological spectrums

Algebraic Geometry 2025-04-01 v2

Abstract

Let XX be a smooth irreducible projective variety over a field k\mathbf{k} of dimension d.d. Let τ:QlC\tau: \mathbb{Q}_l\to \mathbb{C} be any field embedding. Let f:XXf: X\to X be a surjective endomorphism. We show that for every i=0,,2di=0,\dots,2d, the spectral radius of ff^* on the numerical group Ni(X)RN^i(X)\otimes \mathbb{R} and on the ll-adic cohomology group H2i(Xk,Ql)CH^{2i}(X_{\overline{\mathbf{k}}},\mathbb{Q}_l)\otimes \mathbb{C} are the same. As a consequence, if ff is qq-polarized for some q>1q>1, we show that the norm of every eigenvalue of ff^* on the jj-th cohomology group is qj/2q^{j/2} for all j=0,,2d.j=0,\dots, 2d. This generalizes Deligne's theorem for Weil's Riemann Hypothesis to arbitary polarized endomorphisms and proves a conjecture of Tate. We also get some applications for the counting of fixed points and its ``moving target" variant. Indeed we studied the more general actions of certain cohomological coorespondences and we get the above results as consequences in the endomorphism setting.

Keywords

Cite

@article{arxiv.2412.01216,
  title  = {Numerical spectrums control Cohomological spectrums},
  author = {Junyi Xie},
  journal= {arXiv preprint arXiv:2412.01216},
  year   = {2025}
}

Comments

18 pages

R2 v1 2026-06-28T20:19:15.966Z