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Bounds on the Torsion Subgroups of N\'eron-Severi Groups
Algebraic Geometry · Submitted 7 Feb 2019
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We give explicit upper bounds on the order of the torsion subgroup $(\mathrm{NS} \, X)_{\mathrm{tor}}$ of the N\'eron-Severi group of $X$.
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The abstract, sentence by sentence
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.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Let $X \hookrightarrow \mathbb{P}^r$ be a smooth projective variety defined by homogeneous polynomials of degree $\leq d$. | background 0.99 | 0.08 | 0.02 | asserted 0.75 |
| s1 | We give explicit upper bounds on the order of the torsion subgroup $(\mathrm{NS} \, X)_{\mathrm{tor}}$ of the N\'eron-Severi group of $X$. | result 0.53 | 0.97 | 0.88 | asserted 1.00 |
| s2 | 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 $X$. | method 0.99 | 0.90 | 0.11 | asserted 1.00 |
| s3 | 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. | result 0.87 | 0.94 | 0.10 | asserted 1.00 |
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Original 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.
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