Faber's two-point Gromov–Witten relations and Hodge-class identity

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Let XX be a smooth projective variety and let {Ta}\{T_a\} be a basis of H∗(X,Q)H^*(X,\mathbb Q), with dual basis Ta=gabTbT^a=g^{ab}T_b for the Poincaré pairing. Write ⟨⟨⋯ ⟩⟩gX\langle\langle\cdots\rangle\rangle_g^X for the genus-gg Gromov–Witten potential, E\mathbb E for the Hodge bundle, and B2gB_{2g} for the Bernoulli number. Faber's conjecture. For k>gk>g,

∑j=02k(−1)j⟨⟨τj(Ta)τ2k−j(Ta)⟩⟩gX=0.\sum_{j=0}^{2k}(-1)^j\langle\langle\tau_j(T_a)\tau_{2k-j}(T^a)\rangle\rangle_g^X=0.

Moreover,

12∑j=02g−2(−1)j⟨⟨τj(Ta)τ2g−2−j(Ta)⟩⟩g−1=(2g)!B2g⟨⟨ch⁡2g−1(E)⟩⟩g.\frac12\sum_{j=0}^{2g-2}(-1)^j\langle\langle\tau_j(T_a)\tau_{2g-2-j}(T^a)\rangle\rangle_{g-1}=\frac{(2g)!}{B_{2g}}\langle\langle\operatorname{ch}_{2g-1}(\mathbb E)\rangle\rangle_g.

The paper presents these identities in the discussion of the point case and does not provide a resolution of the stated relations.

References

Primary source

Kefeng Liu and Hao Xu, “A proof of the Faber intersection number conjecture”, arXiv:0803.2204 (2009).

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