Chen ranks conjecture for Kähler groups

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Let XX be a compact Kähler manifold. For each g≥2g\geq 2, let E(X)\mathcal{E}(X) be the set of relevant fibrations f ⁣:X→Bff\colon X\to B_f and define

hg(X)=#{f∈E(X):g(Bf)=g}.h_g(X)=\#\big\{f\in\mathcal{E}(X):g(B_f)=g\big\}.

Here Πg\Pi_g denotes the fundamental group of a genus-gg curve, and θq\theta_q denotes the Chen rank. Chen ranks conjecture for Kähler groups. For all q≫0q\gg 0,

θq(π1(X))=∑f∈E(X)θq(π1(Bf))=∑g≥2hg(X)θq(Πg)\theta_q\bigl(\pi_1(X)\bigr)=\sum_{f\in\mathcal{E}(X)}\theta_q(\pi_1(B_f))=\sum_{g\geq 2}h_g(X)\theta_q(\Pi_g)

and hence

θq(π1(X))=(q−1)∑g≥2hg(X)(2g+q−2q)−∑g≥2hg(X)(2g+q−3q−2).\theta_q\bigl(\pi_1(X)\bigr)=(q-1)\sum_{g\geq 2}h_g(X)\binom{2g+q-2}{q}-\sum_{g\geq 2}h_g(X)\binom{2g+q-3}{q-2}.

This is proposed as the natural Chen-ranks formula for Kähler groups, conditional in the surrounding discussion on the expected reducedness of their projective resonance.

References

Primary source

Marian Aprodu, Gavril Farkas, Claudiu Raicu and Alexander I. Suciu, “Reduced resonance schemes and Chen ranks”, arXiv:2303.07855 (2024).

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