Chen ranks conjecture for Kähler groups

From papers

Let XX be a compact Kähler manifold. For each g2g\geq 2, let E(X)\mathcal{E}(X) be the set of relevant fibrations f ⁣:XBff\colon X\to B_f and define

hg(X)=#{fE(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 q0q\gg 0,

θq(π1(X))=fE(X)θq(π1(Bf))=g2hg(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))=(q1)g2hg(X)(2g+q2q)g2hg(X)(2g+q3q2).\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.

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Sources & referencesView supporting material

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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