Erez's conjecture on the square root of the inverse different

Let Fπ/FF_{\pi}/F be a finite Galois-algebra extension of number fields with group GG. Write D(π)\mathfrak{D}(\pi) for its different, and suppose that the square root A(π)A(\pi) of D(π)1\mathfrak{D}(\pi)^{-1} is defined. If Fπ/FF_{\pi}/F is weakly ramified, then A(π)A(\pi) is a locally free ZG\mathbf{Z}G-module and determines a class (A(π))(A(\pi)) in Cl(ZG)\operatorname{Cl}(\mathbf{Z}G). Let Ω(Fπ/F,2)\Omega(F_{\pi}/F,2) denote Chinburg's invariant in this locally free class group. Erez's conjecture. If Fπ/FF_{\pi}/F is weakly ramified, then

(A(π))=Ω(Fπ/F,2).(A(\pi))=\Omega(F_{\pi}/F,2).

This relates the Galois module structure of the square root of the inverse different to Chinburg's equivariant arithmetic invariant. It is known in the tame case, but remains open for general weakly ramified extensions.

Sources & referencesView supporting material

Primary source

A. Agboola, D. Burns, L. Caputo and Y. Kuang, “On the square root of the inverse different”, arXiv:1803.09392 (2022).

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