Leal's ramification bound conjecture for nearby cohomology

Let S\mathcal S be a henselian trait with perfect residue field of characteristic p>0p>0, with closed point ss, generic point η\eta, and geometric generic point η\overline\eta. Let (X,Z)(\mathcal X,\mathcal Z) be a semi-stable pair over S\mathcal S, let f:XSf:\mathcal X\to\mathcal S be proper, and let U=XZ\mathcal U=\mathcal X-\mathcal Z. Let F\mathscr F be a locally constant and constructible sheaf of Λ\Lambda-modules on U\mathcal U whose ramification at generic points of the horizontal part Zf\mathcal Z_f is tame. Let lc(F)\operatorname{lc}(\mathscr F) be the maximum of its logarithmic conductors at generic points of the special fiber Xs\mathcal X_s. Leal's conjecture. The upper-numbering ramification of

RΓc(Uη,FUη)R\Gamma_c(\mathcal U_{\overline\eta},\mathscr F|_{\mathcal U_{\overline\eta}})

is bounded by lc(F)\operatorname{lc}(\mathscr F). Thus the compactly supported étale cohomology of the generic fiber should have no upper-numbering slopes exceeding the largest logarithmic conductor along the special fiber. This is the ramification-bound formulation attributed to Leal and concerns the control of wild monodromy in étale cohomology; the source gives no resolution of the conjecture.

Sources & referencesView supporting material

Primary source

Haoyu Hu, “Semi-continuity of conductors, and ramification bound of nearby cycles”, arXiv:2102.06105 (2022).

Additional references

2 papers in this index state this conjecture (2018–2021). The statement above is taken from the most recent of them; the others are arXiv:1811.02860.

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