The p-adic local invariant cycle conjecture

Let RR be a henselian discrete valuation ring with finite residue field, let RshR^{sh} be a strict henselization, and let KK and KshK^{sh} be the fraction fields of RR and RshR^{sh}. Let I=Gal(K/Ksh)I=\operatorname{Gal}(\overline K/K^{sh}). For a proper flat morphism π:XS=SpecR\pi:{\mathcal X}\longrightarrow S=\operatorname{Spec}R with X{\mathcal X} regular, let XX be its generic fiber, and define

HLi(XRsh,Q(m)):=limnHeti(XRsh,Z(m)etLZ/n)ZQ.H^i_L({\mathcal X}_{R^{sh}},\mathbb{Q}_\ell(m)):=\varprojlim_n \mathbb{H}^i_{\operatorname{et}}({\mathcal X}_{R^{sh}},\mathbb{Z}(m)_{\operatorname{et}}\otimes^{\mathbb L}\mathbb{Z}/\ell^n)\otimes_{\mathbb Z_\ell}\mathbb Q_\ell.

The p-adic local invariant cycle conjecture. If the residue field of RR is finite, there is a surjective natural map

HLi(XRsh,Q(m))Heti(XK,Q(m))I.H^i_L({\mathcal X}_{R^{sh}},\mathbb{Q}_\ell(m))\longrightarrow H^i_{\operatorname{et}}(X_{\overline K},\mathbb{Q}_\ell(m))^I.

This extends the local invariant cycle principle to the motivic or étale Tate-twist setting; the source explains that, under purity of the weight filtration, related surjectivity follows in known cases, but the stated general conjecture remains open.

Sources & referencesView supporting material

Primary source

Yanshuai Qin, “A p-adic local invariant cycle theorem with applications to Brauer groups”, arXiv:2103.04945 (2025).

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