English

Logarithmic double ramification cycles

Algebraic Geometry 2025-03-13 v3

Abstract

Let A=(a1,,an)A=(a_1,\ldots, a_n) be a vector of integers which sum to k(2g2+n)k(2g-2+n). The double ramification cycle DRg,ACHg(Mg,n)\mathsf{DR}_{g,A}\in \mathsf{CH}^g(\mathcal{M}_{g,n}) on the moduli space of curves is the virtual class of an Abel-Jacobi locus of pointed curves (C,x1,,xn)(C,x_1,\ldots,x_n) satisfying OC(i=1naixi)(ωClog)k.\mathcal{O}_C\Big(\sum_{i=1}^n a_i x_i\Big) \, \simeq\, \big(\omega^{\mathsf{log}}_{C}\big)^k\, . The Abel-Jacobi construction requires log blow-ups of Mg,n\mathcal{M}_{g,n} to resolve the indeterminacies of the Abel-Jacobi map. Holmes has shown that DRg,A\mathsf{DR}_{g,A} admits a canonical lift logDRg,AlogCHg(Mg,n)\mathsf{logDR}_{g,A} \in \mathsf{logCH}^g(\mathcal{M}_{g,n}) to the logarithmic Chow ring, which is the limit of the intersection theories of all such blow-ups. The main result of the paper is an explicit formula for logDRg,A\mathsf{logDR}_{g,A} which lifts Pixton's formula for DRg,A\mathsf{DR}_{g,A}. The central idea is to study the universal Jacobian over the moduli space of curves (following Caporaso, Kass-Pagani, and Abreu-Pacini) for certain stability conditions. Using the criterion of Holmes-Schwarz, the universal double ramification theory of Bae-Holmes-Pandharipande-Schmitt-Schwarz applied to the universal line bundle determines the logarithmic double ramification cycle. The resulting formula, written in the language of piecewise polynomials, depends upon the stability condition (and admits a wall-crossing study). Several examples of logarithmic and higher double ramification cycles are computed.

Keywords

Cite

@article{arxiv.2207.06778,
  title  = {Logarithmic double ramification cycles},
  author = {D. Holmes and S. Molcho and R. Pandharipande and A. Pixton and J. Schmitt},
  journal= {arXiv preprint arXiv:2207.06778},
  year   = {2025}
}

Comments

97 pages, 6 figures. Substantial revision following referee reports. Comments very welcome

R2 v1 2026-06-25T00:54:34.253Z