Conjectural splitting of the virtual class for twisted maps to the universal root stack

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Let XX be a smooth pair with boundary divisor DD, let rr be a positive integer, and let Λ\Lambda denote the discrete data of the twisted maps. Write OrbΛ(Ar)\mathrm{Orb}_{\Lambda}(\mathcal{A}_r) for the corresponding moduli space of maps to the universal rr-th root stack, let vd\mathrm{vd} be its virtual dimension, and let Z[τ],Γ′Z_{[\tau],\Gamma'} be strata indexed by types [τ][\tau] and graphs Γ′\Gamma'. For each stratum, let a[τ],Γ′a_{[\tau],\Gamma'} be a coefficient and let C[τ],Γ′C_{[\tau],\Gamma'} be a Chow class depending on rr. Conjectural splitting. There exists an expression

[OrbΛ(Ar)]vir=∑([τ],Γ′)a[τ],Γ′[Z[τ],Γ′]∩C[τ],Γ′[\mathrm{Orb}_{\Lambda}(\mathcal{A}_r)]^{\mathrm{vir}} = \sum_{([\tau], \Gamma')} a_{[\tau], \Gamma'} [Z_{[\tau], \Gamma'}] \cap C_{[\tau], \Gamma'}

where the sum is over strata of dimension at least vd\mathrm{vd} and C[τ],Γ′C_{[\tau],\Gamma'} is a Chow class which is a Laurent polynomial in rr such that

deg⁡r([Z[τ],Γ′])+deg⁡r(C[τ],Γ′)≥0.\operatorname{deg}_r([Z_{[\tau], \Gamma'}]) + \operatorname{deg}_r(C_{[\tau], \Gamma'}) \geq 0.

This proposed decomposition is intended to provide the general structure of the virtual class needed to deduce the polynomiality results for twisted maps to smooth pairs. The source gives no resolution of the conjecture, so its status remains open.

References

Primary source

Robert Crumplin, “Moduli spaces of twisted maps to smooth pairs”, arXiv:2501.15171 (2025).

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