The Brumer–Stark conjecture for Brumer–Stark units

Let FF be a totally real field, let H/FH/F be a finite abelian extension, and let G=Gal(H/F)G=\operatorname{Gal}(H/F). Let RR contain the archimedean places of FF and the places ramified in HH, let pR\mathfrak{p}\notin R split completely in HH, put S=R{p}S=R\cup\{\mathfrak{p}\}, and let TT be an auxiliary finite set disjoint from R{p}R\cup\{\mathfrak{p}\}. For a prime P\mathfrak{P} of HH above p\mathfrak{p}, define

Up={uH:uv=1 if v does not divide p}.\mathcal{U}_{\mathfrak{p}}=\{u\in H^*: |u|_v=1\text{ if }v\text{ does not divide }\mathfrak{p}\}.

Brumer–Stark conjecture. There exists uTUpu_T\in\mathcal{U}_{\mathfrak{p}} such that uT1(modT)u_T\equiv1\pmod T and, for every σG\sigma\in G,

ordP(uTσ)=ζR,T(H/F,σ,0).\operatorname{ord}_{\mathfrak{P}}(u_T^\sigma)=\zeta_{R,T}(H/F,\sigma,0).

Here the absolute-value condition ranges over all finite and archimedean places of HH, and ζR,T(H/F,σ,0)\zeta_{R,T}(H/F,\sigma,0) is the relevant partial zeta value. The conjecture has recently been proved away from 22 in joint work of the first author and Kakde; thus its remaining status is confined to the 22-part.

Sources & referencesView supporting material

Primary source

Samit Dasgupta, Matthew H. L. Honnor and Michael Spieß, “On the Equality of Three Formulas for Brumer–Stark Units”, arXiv:2211.01715 (2025).

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