The local-global cohomological conjecture for relative K-groups

Let FF be a number field and let GG be a finite group on which ΩF\Omega_F acts trivially. Define

Ψ:Ht1(F,G)K0(OFG,Fc),[π][Oπ,OFG;rG],\Psi:H^1_t(F,G)\to K_0(O_FG,F^c),\qquad [\pi]\mapsto[O_\pi,O_FG;{\mathbf r}_G],

and set KR(OFG)=Im(Ψ)K\mathcal R(O_FG)=\operatorname{Im}(\Psi). For each finite place vv of FF, define the local map Ψv\Psi_v analogously, and call an element of K0(OFG,Fc)K_0(O_FG,F^c) cohomological if it lies in Im(Ψ)\operatorname{Im}(\Psi) and locally cohomological if its localisation lies in Im(Ψv)\operatorname{Im}(\Psi_v) for every finite place vv. Let

λ:K0(OFG,Fc)J(K0(OFG,Fc))\lambda:K_0(O_FG,F^c)\to J(K_0(O_FG,F^c))

be the injective localisation map, and let Ψid\Psi^{id} be the induced idelic map. The local-global cohomological conjecture. An element of K0(OFG,Fc)K_0(O_FG,F^c) is cohomological if and only if it is locally cohomological; equivalently,

λ(KR(OFG))=Im(λ)Im(Ψid).\lambda(K\mathcal R(O_FG))=\operatorname{Im}(\lambda)\cap\operatorname{Im}(\Psi^{id}).

This conjecture gives a local-global characterisation of the image of the global resolvend map in relative algebraic KK-theory. The source does not state a resolution; the result is open in this record.

Sources & referencesView supporting material

Primary source

A. Agboola and L. R. McCulloh, “On the relative Galois module structure of rings of integers in tame extensions”, arXiv:1410.4829 (2018).

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