Rationality conjecture for Darmon cohomology classes

Let KK be the real quadratic field, let HO/KH_{\mathcal{O}}/K be the narrow ring class field attached to an order O\mathcal{O}, let VpV_p be the relevant pp-adic representation, and let resp\operatorname{res}_p denote the restriction map from global Mordell–Weil cohomology to local semistable cohomology. For an optimal embedding ΨEmb(O,R)\Psi\in\operatorname{Emb}(\mathcal{O},\mathcal{R}), an ideal class aPic(O)\mathfrak{a}\in\operatorname{Pic}(\mathcal{O}), and a character \Greekmath011F:Gal(HO/K)C×{\Greekmath 011F}:\operatorname{Gal}(H_{\mathcal{O}}/K)\to\mathbb{C}^{\times}, use sΨs_\Psi, saΨs_{\mathfrak{a}\star\Psi}, and s\Greekmath011Fs_{\Greekmath 011F} for the associated Darmon cohomology classes. Rationality conjecture.

  1. For every optimal embedding ΨEmb(O,R)\Psi\in\operatorname{Emb}(\mathcal{O},\mathcal{R}), there is a global class sΨMW(HO,Vp)\underline{s}_\Psi\in\operatorname{MW}_*(H_{\mathcal{O}},V_p) such that
sΨ=resp(sΨ).s_\Psi=\operatorname{res}_p(\underline{s}_\Psi).
  1. For every Ψ\mathpalette\overrightarrow@Emb+(O,R)\Psi\in\mathpalette\overrightarrow@{\operatorname{Emb}}_+(\mathcal{O},\mathcal{R}) and every aPic(O)\mathfrak{a}\in\operatorname{Pic}(\mathcal{O}), if \Greekmath011B=rec(a)1Gal(HO/K){\Greekmath 011B}=\operatorname{rec}(\mathfrak{a})^{-1}\in\operatorname{Gal}(H_{\mathcal{O}}/K), then
resp(\Greekmath011BsΨ)=saΨ.\operatorname{res}_p({}^{{\Greekmath 011B}}\underline{s}_\Psi)=s_{\mathfrak{a}\star\Psi}.
  1. For every character \Greekmath011F:Gal(HO/K)C×{\Greekmath 011F}:\operatorname{Gal}(H_{\mathcal{O}}/K)\to\mathbb{C}^{\times}, there is a class s\Greekmath011FMW\Greekmath011F(H\Greekmath011F,Vp)\underline{s}_{\Greekmath 011F}\in\operatorname{MW}^{{\Greekmath 011F}}(H_{\Greekmath 011F},V_p) such that
s\Greekmath011F=resp(s\Greekmath011F),s_{\Greekmath 011F}=\operatorname{res}_p(\underline{s}_{\Greekmath 011F}),

where H\Greekmath011F/KH_{\Greekmath 011F}/K is the abelian subextension cut out by \Greekmath011F{\Greekmath 011F} and MW\Greekmath011F\operatorname{MW}^{{\Greekmath 011F}} denotes its \Greekmath011F{\Greekmath 011F}-isotypical subspace.

The conjecture predicts that locally defined Darmon classes arise by restriction from global cohomology classes and satisfy the expected reciprocity law. The text explicitly notes that part (3) follows from parts (1) and (2); no resolution is supplied.

Sources & referencesView supporting material

Primary source

Victor Rotger and Marco Adamo Seveso, “L-invariants and Darmon cycles attached to modular forms”, arXiv:1004.3513 (2010).

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