Rigid Clemens–Schmidt conjecture for limiting Frobenius structures

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Let X→S⊆AFq1∖{0}X\to S\subseteq \mathbb A^1_{\mathbb F_q}\setminus\{0\} be a morphism of varieties over Fq\mathbb F_q with a good lift around t=0t=0. Let (H0m,N0,F0,em)({\mathcal H}_0^m,{\mathcal N}_0,{\mathcal F}_0,e_m) be the limiting Frobenius structure at t=0t=0 in dimension mm, and define

e=lcm⁡0≤m≤2n(em).e=\operatorname{lcm}_{0\leq m\leq 2n}(e_m).

Let Xe→SeX_e\to S_e be obtained by pulling back along Se→SS_e\to S. Rigid Clemens–Schmidt conjecture. The morphism Xe→SeX_e\to S_e extends to a semistable degeneration with degenerate fibre Xe,0X_{e,0} and, for every such extension, there exists a covariant rigid homology functor Hj,rig⁡(∙)H_{j,\operatorname{rig}}(\bullet) on semistable Fq\mathbb F_q-varieties, vanishing outside 0≤j≤2n0\leq j\leq 2n, for which an exact sequence of FF-isocrystals contains

⋯→H2n+2−m,rig⁡(Xe,0)(−n−1)→Hrig⁡m(Xe,0)→H0m→N0H0m(−1)\cdots\to H_{2n+2-m,\operatorname{rig}}(X_{e,0})(-n-1)\to H^m_{\operatorname{rig}}(X_{e,0})\to {\mathcal H}_0^m\xrightarrow{{\mathcal N}_0}{\mathcal H}_0^m(-1) →H2n−m,rig⁡(Xe,0)(−n−1)→Hrig⁡m+2(Xe,0)→H0m+2→N0H0m+2(−1)→⋯ .\to H_{2n-m,\operatorname{rig}}(X_{e,0})(-n-1)\to H^{m+2}_{\operatorname{rig}}(X_{e,0})\to {\mathcal H}_0^{m+2}\xrightarrow{{\mathcal N}_0}{\mathcal H}_0^{m+2}(-1)\to\cdots.

This is the rigid-cohomological analogue of the Clemens–Schmidt sequence for complex semistable degenerations and would give the limiting Frobenius structure the predicted geometric meaning.

References

Primary source

Alan G. B. Lauder, “Degenerations and limit Frobenius structures in rigid cohomology”, arXiv:0912.5185 (2009).

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