Improving the trivial bound for $\ell$-torsion in class groups

Fuente: arXiv
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Autori principali: Oliver, Robert J. Lemke, Zaman, Asif
Natura: Preprint
Pubblicazione: 2025
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author Oliver, Robert J. Lemke
Zaman, Asif
author_facet Oliver, Robert J. Lemke
Zaman, Asif
contents For any number field $K$ with $D_K=|\mathrm{Disc}(K)|$ and any integer $\ell \geq 2$, we improve over the commonly cited trivial bound $|\mathrm{Cl}_K[\ell]| \leq |\mathrm{Cl}_K| \ll_{[K:\mathbb{Q}],\varepsilon} D_K^{1/2+\varepsilon}$ on the $\ell$-torsion subgroup of the class group of $K$ by showing that $|\mathrm{Cl}_K[\ell]| = o_{[K:\mathbb{Q}],\ell}(D_K^{1/2})$. In fact, we obtain an explicit log-power saving. This is the first general unconditional saving over the trivial bound that holds for all $K$ and all $\ell$.
format Preprint
id arxiv_https___arxiv_org_abs_2502_03464
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Improving the trivial bound for $\ell$-torsion in class groups
Oliver, Robert J. Lemke
Zaman, Asif
Number Theory
11R29, 11R42
For any number field $K$ with $D_K=|\mathrm{Disc}(K)|$ and any integer $\ell \geq 2$, we improve over the commonly cited trivial bound $|\mathrm{Cl}_K[\ell]| \leq |\mathrm{Cl}_K| \ll_{[K:\mathbb{Q}],\varepsilon} D_K^{1/2+\varepsilon}$ on the $\ell$-torsion subgroup of the class group of $K$ by showing that $|\mathrm{Cl}_K[\ell]| = o_{[K:\mathbb{Q}],\ell}(D_K^{1/2})$. In fact, we obtain an explicit log-power saving. This is the first general unconditional saving over the trivial bound that holds for all $K$ and all $\ell$.
title Improving the trivial bound for $\ell$-torsion in class groups
topic Number Theory
11R29, 11R42
url https://arxiv.org/abs/2502.03464