Esnault–Kerz conjecture on curvewise computation of the Swan divisor

Let XX be a normal κ\kappa-scheme of finite type, let DD be an integral effective Cartier divisor with smooth complement U=XDU=X-D, and let j:UXj:U\rightarrow X be the canonical injection. Let F\mathscr F be a locally constant constructible sheaf of Λ\Lambda-modules on UU, and let C(X)\mathcal C(X) be the set of canonical morphisms g:C~Xg:\widetilde C\rightarrow X from normalizations of suitable one-dimensional integral closed subschemes. Define PC(X)\mathcal{PC}(X) as the set of pairs (g:C~X,x)(g:\widetilde C\rightarrow X,x) with gC(X)g\in\mathcal C(X) and xx a closed point of gDg^*D. Write mx(gD)m_x(g^*D) for the multiplicity of gDg^*D at xx, and let swD(j!F)\mathrm{sw}_D(j_!\mathscr F) be the coefficient of the Swan divisor after replacing XX by a smooth open neighborhood of the generic point of DD.

Esnault–Kerz conjecture. One has

supPC(X)swx(gj!F)mx(gD)=swD(j!F).\sup_{\mathcal{PC}(X)}\frac{\mathrm{sw}_x(g^*j_!\mathscr F)}{m_x(g^*D)}=\mathrm{sw}_D(j_!\mathscr F).

The conjecture asserts that the generic coefficient of the Swan divisor is recovered exactly as the supremum of normalized curvewise Swan conductors. It is the sharp curve-restriction formulation of the logarithmic ramification prediction described in the source.

Sources & referencesView supporting material

Primary source

Haoyu Hu, “Logarithmic ramifications of étale sheaves by restricting to curves”, arXiv:1704.04734 (2017).

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