Spin Euler-characteristic ratio conjecture for minimal strata

Let Mg(2g1)\mathcal{M}_g(2g-1) be the minimal stratum of differentials, let χ(Mg(2g1))spin\chi(\mathcal{M}_g(2g-1))^{\rm spin} denote its spin Euler characteristic, and let χ(Mg(2g1)even)\chi(\mathcal{M}_g(2g-1)^{\rm even}) and χ(Mg(2g1)odd)\chi(\mathcal{M}_g(2g-1)^{\rm odd}) denote the Euler characteristics of its even and odd components. Spin asymptotic conjecture. There exist positive constants AA and BB such that

Ag2g<χ(Mg(2g1))spinχ(Mg(2g1))<Bg22gA\frac{g}{2^g}<\frac{\chi(\mathcal{M}_g(2g-1))^{\rm spin}}{-\chi(\mathcal{M}_{g}(2g-1))}<B\frac{g^2}{2^g}

for all gg. In particular, χ(Mg(2g1))spin>0\chi(\mathcal{M}_g(2g-1))^{\rm spin}>0 and

χ(Mg(2g1)even)χ(Mg(2g1)odd)1for g.\frac{\chi(\mathcal{M}_g(2g-1)^{\rm even})}{\chi(\mathcal{M}_g(2g-1)^{\rm odd})}\longrightarrow 1\quad\text{for }g\longrightarrow\infty.

This stronger conjecture implies the preceding asymptotic equivalence of the Euler characteristics of the odd and even components and concerns the large-genus behavior of spin strata.

Sources & referencesView supporting material

Primary source

Matteo Costantini, Adrien Sauvaget and Johannes Schmitt, “Integrals of ψ-classes on twisted double ramification cycles and spaces of differentials”, arXiv:2112.04238 (2025).

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