Volume 87, Nº 3 (2023)

Let $L$ be a complete discrete valuation field of prime characteristic $p$ with finite residue field. Denote by $\Gamma_{L}^{(v)}$ the ramification subgroups of $\Gamma_{L}=\operatorname{Gal}(L^{\mathrm{sep}}/L)$. We consider the category $\operatorname{M\Gamma}_{L}^{\mathrm{Lie}}$ of finite $\mathbb{Z}_p[\Gamma_{L}]$-modules $H$, satisfying some additional (Lie)-condition on the image of $\Gamma_L$ in $\operatorname{Aut}_{\mathbb{Z}_p}H$. In the paper it is proved that all information about the images of the groups $\Gamma_L^{(v)}$ in $\operatorname{Aut}_{\mathbb{Z}_p}H$ can be explicitly extracted from some differential forms $\widetilde{\Omega} [N]$ on the Fontaine etale $\phi $-module $M(H)$ associated with $H$. The forms $\widetilde{\Omega}[N]$ are completely determined by a canonical connection $\nabla $ on $M(H)$. In the case of fields $L$ of mixed characteristic, which contain a primitive $p$th root of unity, we show that a similar problem for $\mathbb{F}_p[\Gamma_L]$-modules also admits a solution. In this case we use the field-of-norms functor to construct the corresponding $\phi $-module together with the action of the Galois group of a cyclic extension $L_1$ of $L$ of degree $p$. Then our solution involves the characteristic $p$ part (provided by the field-of-norms functor) and the condition for a “good” lift of a generator of $\operatorname{Gal}(L_1/L)$. Apart from the above differential forms the statement of this condition uses the power series coming from the $p$-adic period of the formal group $\mathbb{G}_m$.Bibliography: 21 titles.

We construct non-isogenous simple ordinary abelian varieties over an algebraic closure of a finite field with isomorphic endomorphism algebras.

In the article, we give a presentation of the fundamental group of the complement to a curve $C$ in its "tubular"  neighborhood in a normal surface $S$. The presentation is given in terms of the double weighted dual graph of a resolution of singularities of $C$ (and $S$)and it is a generalization of the presentation of the fundamental group of the complement to a normal singularity in its neighborhood given by Mumford in the case when the dual graph of resolution is a tree and all exceptional curves of the resolution are rational curves.

Present paper continues the investigations in special Bohr–Sommerfeld lagrangian geometry of compact symplectic manifolds. Using natural deformation parameters we avoid the difficulties arose in the definition of the moduli space of special Bohr–Sommerfeld cycles for compact simply connected algebraic varieties. As an application one presents remarks which show how our construction can be exploited in the study of the Weinstein structures and a conjecture of Eliashberg.