Liu–Xu Hodge-integral conjecture

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Let g≥2g\geq2, let nn be a positive integer, and let dj≥1d_j\geq1 satisfy

∑j=1n(dj−1)=g.\sum_{j=1}^{n}(d_j-1)=g.

Let λi\lambda_i denote the Chern classes of the Hodge bundle, let τd\tau_d denote a psi-class insertion, let B2g−2B_{2g-2} be the Bernoulli number, and write ⟨∏j=1nτdj∣λaλb⟩g\langle\prod_{j=1}^n\tau_{d_j}\mid\lambda_a\lambda_b\rangle_g for the corresponding Hodge integral. Liu–Xu's Hodge-integral conjecture.

2g−2∣B2g−2∣(⟨∏j=1nτdj∣λg−1λg−2⟩g−3⟨∏j=1nτdj∣λg−3λg⟩g)=12∑j=02g−4(−1)j⟨τ2g−4−jτj∏i=1nτdi⟩g−1+(2g−3+n)!22g+1(2g−3)!∏j=1n(2dj−1)!!.\frac{2g-2}{|B_{2g-2}|}\left(\left\langle\prod_{j=1}^n\tau_{d_j}\mid\lambda_{g-1}\lambda_{g-2}\right\rangle_g-3\left\langle\prod_{j=1}^n\tau_{d_j}\mid\lambda_{g-3}\lambda_g\right\rangle_g\right)=\frac{1}{2}\sum_{j=0}^{2g-4}(-1)^j\left\langle\tau_{2g-4-j}\tau_j\prod_{i=1}^n\tau_{d_i}\right\rangle_{g-1}+\frac{(2g-3+n)!}{2^{2g+1}(2g-3)!\prod_{j=1}^n(2d_j-1)!!}.

The source presents this as an identity equivalent to the preceding conjectural psi-intersection formula, using the relation between ch⁡2g−3(E)\operatorname{ch}_{2g-3}(\mathbb E) and Hodge classes; no resolution is given in the supplied text.

References

Primary source

Kefeng Liu and Hao Xu, “New results of intersection numbers on moduli spaces of curves”, arXiv:0705.3564 (2007).

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