Toric pullback irreducibility conjecture for finite maps

Let WW be an irreducible quasiprojective variety and let φ ⁣:WGmn\varphi\colon W\to\mathbb{G}_{\rm m}^n be a map finite onto its image. Let φ(W)\overline{\varphi(W)} denote the closure of its image.

Toric pullback irreducibility conjecture. There is a finite union E\mathcal{E} of proper subtori of Gmn\mathbb{G}_{\rm m}^n and a finite set Λ\Lambda of isogenies of Gmn\mathbb{G}_{\rm m}^n such that, for every subtorus TGmnT\subset\mathbb{G}_{\rm m}^n satisfying

dim(T)codim(φ(W))+1\dim(T)\geq\operatorname{codim}(\overline{\varphi(W)})+1

and every point pGmn(C)p\in\mathbb{G}_{\rm m}^n(\mathbb{C}), one of the following holds: TET\subseteq\mathcal{E}; there is λΛ\lambda\in\Lambda such that λW\lambda^*W is reducible and a subtorus TGmnT'\subset\mathbb{G}_{\rm m}^n on which λ\lambda induces an isomorphism TTT'\to T; or φ1(pT)\varphi^{-1}(p\cdot T) is irreducible.

This conjecturally extends the preceding toric Bertini statement by allowing reducibility to be detected after finitely many isogeny pullbacks. Its status is not resolved in the supplied text.

Sources & referencesView supporting material

Primary source

Francesco Amoroso and Martín Sombra, “Factorization of bivariate sparse polynomials”, arXiv:1710.11479 (2018).

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