A zero-part formula for logarithmic double ramification intersections

Let dd be the degree, let ν\boldsymbol{\nu} be the ramification data, and let logDR0(d,ν)\operatorname{logDR}_0(d,-\boldsymbol{\nu}) denote the logarithmic double ramification cycle. Let ψ1\psi_1 be the cotangent-line class at the first marking and let branchm1e\operatorname{branch}_{m-1-e} be the corresponding branch class. Zero-part formula. After inserting ν1=0\nu_1=0,

logDR0(d,ν)ψ1ebranchm1eν1=0=(m1e)(m2)!(e+1)!(i=1e+1j=0me3(d(i+j)k2)).\int_{\operatorname{logDR}_0(d,-\boldsymbol{\nu})} \psi_1^{e}\cdot \operatorname{branch}_{m-1-e}\big|_{\nu_1=0} =(m-1-e)\frac{(m-2)!}{(e+1)!} \cdot \Big( \sum_{i=1}^{e+1} \prod_{j=0}^{m-e-3}(d-(i+j)\frac{k}{2})\Big).

The formula is introduced as a conjectural expression obtained by inserting a contracted marked point into the recursion. The text notes that it currently has no geometric meaning in this form, while suggesting that it should acquire one.

Sources & referencesView supporting material

Primary source

Renzo Cavalieri, Hannah Markwig and Johannes Schmitt, “One part leaky covers”, arXiv:2509.04335 (2025).

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