Uniform torsion-freeness conjecture for smooth projective varieties

Let XPNX\subset\mathbb{P}^{N} be a smooth, projective variety of dimension nn and degree DD over an algebraically closed field kk. For a prime number \ell coprime to the characteristic of kk, consider the torsion subgroup Hi(X,Z)tors\mathrm{H}^{i}(X,\mathbb{Z}_{\ell})_{\mathrm{tors}} of its \ell-adic cohomology.

Uniform torsion-freeness conjecture. There exist polynomials ψ(x),ϕ(x)Z[x]\psi(x),\phi(x)\in\mathbb{Z}[x] such that

Hi(X,Z)tors=0\mathrm{H}^{i}(X,\mathbb{Z}_{\ell})_{\mathrm{tors}}=0

for 0i2n0\leq i\leq 2n whenever

>ψ(Dϕ(N))\ell>\psi\bigl(D^{\phi(N)}\bigr)

is a prime number coprime to the characteristic of kk.

This conjecture proposes a uniform bound, polynomial in DD and controlled by NN, beyond which the integral \ell-adic cohomology is torsion-free. It is motivated by bounds on Betti numbers and by Gabber's torsion-freeness theorem, which gives torsion-freeness for all but finitely many \ell in positive characteristic; the stated uniform bound over arbitrary algebraically closed fields remains open.

Sources & referencesView supporting material

Primary source

Hyuk Jun Kweon and Madhavan Venkatesh, “Bornes de torsion et un théorème effectif du pgcd”, arXiv:2511.00431 (2025).

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