Faber's intersection number conjecture in ψ\psi-form

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Let Mg,nrt{\mathcal M}_{g,n}^{rt} be the moduli space of stable nn-pointed genus-gg curves with rational tails, and let

π:Mg,nrt⟶Mg,1\pi:{\mathcal M}_{g,n}^{rt}\longrightarrow {\mathcal M}_{g,1}

be the forgetful morphism. For positive integers d1,…,dnd_1,\ldots,d_n, write (2a−1)!!=1⋅3⋯(2a−1)=(2a)!/(2aa!)(2a-1)!!=1\cdot3\cdots(2a-1)=(2a)!/(2^a a!). Faber's intersection number conjecture. For every nn-tuple of positive integers (d1,…,dn)(d_1,\ldots,d_n) satisfying ∑idi=g−2+n\sum_i d_i=g-2+n, one has

π∗(ψ1d1⋯ψndn)=(2g−3+n)!(2g−1)!!(2g−1)!∏j=1n(2dj−1)!! ψ1g−1.\pi_*\left(\psi_1^{d_1}\cdots\psi_n^{d_n}\right)=\frac{(2g-3+n)!(2g-1)!!}{(2g-1)!\prod_{j=1}^n(2d_j-1)!!}\,\psi_1^{g-1}.

This is a proposed explicit formula for tautological intersection classes on the rational-tails locus and is the ψ\psi-class form of Faber's intersection number conjecture. The supplied text does not establish its resolution.

References

Primary source

Ian P. Goulden, David M. Jackson and Ravi Vakil, “The moduli space of curves, double Hurwitz numbers, and Faber's intersection number conjecture”, arXiv:math/0611659 (2006).

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