Rigid Clemens–Schmidt conjecture for limiting Frobenius structures

From papers

Let XSAFq1{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=lcm0m2n(em).e=\operatorname{lcm}_{0\leq m\leq 2n}(e_m).

Let XeSeX_e\to S_e be obtained by pulling back along SeSS_e\to S. Rigid Clemens–Schmidt conjecture. The morphism XeSeX_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 0j2n0\leq j\leq 2n, for which an exact sequence of FF-isocrystals contains

H2n+2m,rig(Xe,0)(n1)Hrigm(Xe,0)H0mN0H0m(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) H2nm,rig(Xe,0)(n1)Hrigm+2(Xe,0)H0m+2N0H0m+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.

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Sources & referencesView supporting material

Primary source

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

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