# Bounds on the Torsion Subgroups of N\'eron-Severi Groups

## TL;DR

This paper provides explicit upper bounds on the torsion subgroup of the Néron-Severi group for smooth projective varieties defined by polynomials of bounded degree, based on bounds for certain Hilbert and divisor schemes.

## Contribution

It introduces explicit bounds on the torsion of the Néron-Severi group using bounds on the components of Hilbert and divisor schemes.

## Key findings

- Explicit upper bounds on the torsion subgroup size.
- Bounds on the number of generators of the torsion subgroup for primes not dividing the characteristic.
- Quantitative estimates for the structure of the Néron-Severi group.

## Abstract

Let $X \hookrightarrow \mathbb{P}^r$ be a smooth projective variety defined by homogeneous polynomials of degree $\leq d$. We give explicit upper bounds on the order of the torsion subgroup $(\mathrm{NS} \, X)_{\mathrm{tor}}$ of the N\'eron-Severi group of $X$. The bounds are derived from an explicit upper bound on the number of irreducible components of either the Hilbert scheme $\mathbf{Hilb}_Q X$ or the scheme $\mathbf{CDiv}_n X $parametrizing the effective Cartier divisors of degree $n$ on $X$. We also give an upper bound on the number of generators of $(\mathrm{NS} \, X)[\ell^\infty]$ uniform as $\ell \neq \mathrm{char}\, k$ varies.