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

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,nrtMg,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 (2a1)!!=13(2a1)=(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=g2+n\sum_i d_i=g-2+n, one has

π(ψ1d1ψndn)=(2g3+n)!(2g1)!!(2g1)!j=1n(2dj1)!!ψ1g1.\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.

Sources & referencesView supporting material

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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