Hain's conjecture on NMHS structures on relative Malcev completions

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Let XX be a pointed space with fundamental group π1(X,x)\pi_1(X,x), let V\mathcal V be a variation of Hodge structure with fibre Vx\mathcal V_x and polarization ⟨⋅,⋅⟩\langle\cdot,\cdot\rangle, and let

ρ:π1(X,x)→Aut⁡(Vx,⟨⋅,⋅⟩)\rho:\pi_1(X,x)\to \operatorname{Aut}(\mathcal V_x,\langle\cdot,\cdot\rangle)

be its monodromy representation. Let SS be the Zariski closure of the image of ρ\rho, and let G\mathscr G be the relative Malcev completion of π1(X,x)\pi_1(X,x) with respect to the induced representation into SS.

Hain's conjecture. The relative completion G\mathscr G should carry a nonabelian mixed Hodge structure in general. This structure should be a quotient of π1hodge(X,x)\pi_1^{\mathrm{hodge}}(X,x).

Hain proved this assertion when the monodromy representation has Zariski-dense image in the relevant reductive algebraic group. The conjectural extension concerns the case where the target is the Zariski closure of the monodromy image.

References

Primary source

Donu Arapura, “The Hodge theoretic fundamental group and its cohomology”, arXiv:0902.4252 (2009).

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