Cohomological p-newness conjecture for Eisenstein congruence classes

Let N,M1N,M\geq 1 be fixed coprime square-free integers, let ψ\psi and ϕ\phi be characters of conductors u,v1u,v\geq 1 with uv=Nuv=N, and let λ\lambda' be a prime above ll. Define

Ck,lψ,ϕ=(Ql/Zl)(1k)(ψ1ϕ).C_{k,l}^{\psi,\phi}= (\mathbb{Q}_l/\mathbb{Z}_l)(1-k)(\psi^{-1}\phi).

Let PNM\mathcal{P}_{NM} denote the set of prime divisors of NMNM, and let cHPNM1(Q,Ck,lψ,ϕ)c'\in H^1_{\mathcal{P}_{NM}}(\mathbb{Q},C_{k,l}^{\psi,\phi}) be the class supplied by the Eisenstein congruence. Set

S=pPMordλ(ψ(p)ϕ(p)pk)>0.\mathcal{S}=\\{p\in\mathcal{P}_M\mid \operatorname{ord}_{\lambda'}(\psi(p)-\phi(p)p^k)>0\\}.

Cohomological p-newness conjecture. The class cc' is pp-new for every pSp\in\mathcal{S}, meaning that it does not come from the corresponding relaxed Selmer group with the condition at pp removed. The conjecture predicts that the cohomology class arising from the congruence records the newness at every prime whose local Euler factor contributes to the congruence. The source presents this as a conjecture after noting that the preceding conditions guarantee only pp-newforms separately, rather than a genuine newform; no general proof is given.

Sources & referencesView supporting material

Primary source

Dan Fretwell and Jenny Roberts, “Newform Eisenstein Congruences of Local Origin”, arXiv:2306.09842 (2026).

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