A Manin-type conjecture for Campana Fano orbifolds

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Let (X,Dϵ)(X,D_\epsilon) be a Campana orbifold over a number field FF such that −(KX+Dϵ)-(K_X+D_\epsilon) is ample, and let (X,Dϵ)(\mathcal X,\mathcal D_\epsilon) be a good integral model over the ring of SS-integers OF,S\mathcal O_{F,S}, where SS contains all archimedean places. Assume ⌊Dϵ⌋=0\lfloor D_\epsilon\rfloor=0, so the orbifold is klt, and let HL\mathsf H_{\mathcal L} be the height associated with an adelically metrized big line bundle L=(L,∥⋅∥)\mathcal L=(L,\|\cdot\|), with counting function

N(U,L,T)=#{P∈U∣HL(P)≤T}.\mathsf N(U,\mathcal L,T)=\#\{P\in U\mid \mathsf H_{\mathcal L}(P)\leq T\}.

Suppose that LL is nef and that the set of klt Campana points (X,Dϵ)(OF,S)(\mathcal X,\mathcal D_\epsilon)(\mathcal O_{F,S}) is not thin. Manin-type conjecture for Fano orbifolds. There exists a thin set Z⊂(X,Dϵ)(OF,S)Z\subset(\mathcal X,\mathcal D_\epsilon)(\mathcal O_{F,S}) such that

N((X,Dϵ)(OF,S)∖Z,L,T)∼c(F,S,(X,Dϵ),L,Z)Ta((X,Dϵ),L)(log⁡T)b(F,(X,Dϵ),L)−1\mathsf N\bigl((\mathcal X,\mathcal D_\epsilon)(\mathcal O_{F,S})\setminus Z,\mathcal L,T\bigr)\sim c(F,S,(\mathcal X,\mathcal D_\epsilon),\mathcal L,Z)T^{a((X,D_\epsilon),L)}(\log T)^{b(F,(X,D_\epsilon),L)-1}

as T→∞T\to\infty, where

a((X,Dϵ),L)=inf⁡{t∈R∣tL+KX+Dϵ∈Eff⁡1(X)a((X,D_\epsilon),L)=\inf\{t\in\mathbb R\mid tL+K_X+D_\epsilon\in\operatorname{Eff}^1(X)

is the Fujita invariant, and b(F,(X,Dϵ),L)b(F,(X,D_\epsilon),L) is the codimension of the minimal supported face of Eff⁡1(X)\operatorname{Eff}^1(X) containing a((X,Dϵ),L)[L]+[KX+Dϵ]a((X,D_\epsilon),L)[L]+[K_X+D_\epsilon]. The constant c(F,S,(X,Dϵ),L,Z)c(F,S,(\mathcal X,\mathcal D_\epsilon),\mathcal L,Z) is a positive Tamagawa constant.

References

Primary source

Marta Pieropan, Arne Smeets, Sho Tanimoto and Anthony Várilly-Alvarado, “Campana points of bounded height on vector group compactifications”, arXiv:1908.10263 (2020).

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