Gross's explicit reciprocity conjecture for Brumer–Stark units

Let H/FH/F be as in the Brumer–Stark setting, let L/FL/F be a finite abelian CM extension containing HH, and write g=Gal(L/F)\mathfrak{g}=\operatorname{Gal}(L/F) and Γ=Gal(L/H)\Gamma=\operatorname{Gal}(L/H). Let II be the relative augmentation ideal for gG=Gal(H/F)\mathfrak{g}\twoheadrightarrow G=\operatorname{Gal}(H/F), and let upu_{\mathfrak p} be the Brumer–Stark unit attached to a prime p\mathfrak p splitting completely in HH. Define

recG(up)=σG(recPσ(up)1)σ~1I/I2,\operatorname{rec}_G(u_{\mathfrak p})=\sum_{\sigma\in G}(\operatorname{rec}_{\mathfrak P}\sigma(u_{\mathfrak p})-1)\widetilde\sigma^{-1}\in I/I^2,

where σ~\widetilde\sigma is any lift of σ\sigma. Gross's conjecture. One should have

recG(up)ΘS,TL/F(modI2),\operatorname{rec}_G(u_{\mathfrak p})\equiv\Theta_{S',T}^{L/F}\pmod{I^2},

viewed as an equality in I/I2I/I^2. This conjecture gives an explicit reciprocity-law interpretation of the first-order augmentation derivative of a Stickelberger element in terms of Brumer–Stark units. The source gives no resolution status.

Sources & referencesView supporting material

Primary source

Samit Dasgupta and Mahesh Kakde, “On the Brumer-Stark Conjecture and Refinements”, arXiv:2204.09037 (2022).

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