Abstract
We define various formal moduli spaces of p-divisible groups which are regular, and morphisms between them. We formulate arithmetic transfer conjectures, which are variants of the arithmetic fundamental lemma conjecture of the third author in the presence of ramification. These conjectures include the AT conjecture of our previous joint work. We prove these conjectures in low-dimensional cases.
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Notes
Recall that, since \(F/F_0\) is unramified, we have \(\breve{F}=\breve{F}_0\) as in the Introduction.
Recall that essentially proper means that each irreducible component of the reduced underlying scheme is proper over \({{\mathrm{Spec}}}\overline{k}\).
Here and below we replace the symbol W used in loc. cit. with .
Here and below we interchange r and s in the notation relative to [32].
Note that the statement in loc. cit. considers quasi-isogenies which are compatible with the polarizations only up to scalar, whereas here we are requiring compatibility on the nose.
Strictly speaking, loc. cit. shows these these implications hold in the case of signature opposite to ours, but up to isomorphism the local model is the same, cf. [24, p. 19 fn. 5]. The same remark applies to essentially all of the subsequent references we make to the local models in [3, 20], [21, §2.6], and [32].
Exceptional in three ways: in this case the space is defined over \({{\mathrm{Spf}}}O_{\breve{F}_0}\) instead of \({{\mathrm{Spf}}}O_{\breve{F}}\); it is regular; and the corresponding parahoric subgroup of \(\text {GU}(h)(F_0)\) is not a maximal parahoric subgroup, but an Iwahori subgroup, cf. [21, Rem. 2.35].
Note that later on, for technical convenience, we will rescale the polarization \(\lambda _\mathbb {X} \), cf. Example 9.4.
Note that the quantity \(\eta \) in loc. cit. should be a square root of \(-\epsilon ^{-1}\), rather than a square root of \(\epsilon ^{-1}\).
Here the condition \(VL' \subset ^{\le 1} VL' + \pi L'\) is manifestly equivalent to the wedge condition in the moduli problem for \(\mathcal {P} _n\), via the canonical isomorphism \({{\mathrm{Lie\,}}}X' \cong L'/VL'\). For the purposes of the proof, we only need to know that the moduli problem implies this condition on \(L'\); we leave it as an exercise to show that, for \(\overline{k}\)-points, condition (9.2) imposes nothing further.
Here conditions (6) and (7) make sense as written whenever S is an \(O_F\)-scheme, and when \(r = s\) they descend to conditions on \(M_I^\text {naive} \) over \({{\mathrm{Spec}}}O_E = {{\mathrm{Spec}}}O_{F_0}\).
Strictly speaking loc. cit. requires I to have the property that if n is even and \(m - 1 \in I\), then \(m \in I\), but here we drop this requirement. Note that on the other hand, Proposition 9.12 below allows one to view sets I not satisfying this property as being redundant in some sense.
When \((r,s) = (1,1)\), these schemes are defined over \({{\mathrm{Spec}}}O_{F_0}\), and here we implicitly replace them with their base change to \({{\mathrm{Spec}}}O_F\).
After extension of scalars, this becomes an Iwahori subgroup.
Note that in loc. cit. n is odd, which in the case of our \(\widetilde{\eta }\) implies that \(\widetilde{\eta }(\gamma _1^{-1}\gamma _2)^{n-1} = 1\); however the proof for arbitrary n is analogous. The last statement in (iv) is immediate from the specific choice of \(\phi _\mathrm {corr}'\) given in (5.13) in loc. cit.
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Acknowledgements
We are grateful to U. Görtz, X. He, and S. Yu for helpful discussions. We also acknowledge the hospitality of the ESI (Vienna) and the MFO (Oberwolfach), where part of this work was carried out. We finally thank the referee for his/her remarks on the text. M.R. is supported by a Grant from the Deutsche Forschungsgemeinschaft through the Grant SFB/TR 45. B.S. is supported by a Simons Foundation Grant #359425 and an NSA Grant H98230-16-1-0024. W.Z. is supported by NSF Grants DMS #1301848 and #1601144, and by a Sloan research fellowship.
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Communicated by Toby Gee.
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Rapoport, M., Smithling, B. & Zhang, W. Regular formal moduli spaces and arithmetic transfer conjectures. Math. Ann. 370, 1079–1175 (2018). https://doi.org/10.1007/s00208-017-1526-2
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DOI: https://doi.org/10.1007/s00208-017-1526-2