Density conjecture for geometric-origin representations

Let GG be a linear algebraic group over the complex numbers, let XX be a normal complex variety with base point xx, and write

π=π1(X(C),x),ChG,C(π)\pi=\pi_1(X(\mathbb C),x),\qquad {\rm Ch}_{G,\mathbb C}^{\Box}(\pi)

for the framed character variety of GG-representations of π\pi. Fix an embedding GGLr,CG\hookrightarrow \operatorname{GL}_{r,\mathbb C}. A GG-representation is of geometric origin if, after restriction to a suitable dense open subvariety and semisimplification, its associated linear local system is a direct summand of a local system arising from the higher direct images of a smooth projective morphism.

Density conjecture. The set of GG-representations of geometric origin is Zariski dense in

ChG,C(π).{\rm Ch}_{G,\mathbb C}^{\Box}(\pi).

This conjecture concerns the density of representations arising from geometry in framed character varieties. The source notes that it holds when GG is abelian, by the torus case of Esnault--Kerz, while Landesman and Litt showed that it is false in this generality because of rank obstructions for geometric local systems with infinite monodromy on certain curves.

Sources & referencesView supporting material

Primary source

Hélène Esnault and Moritz Kerz, “Local systems with quasi-unipotent monodromy at infinity are dense”, arXiv:2101.00487 (2022).

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