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Bruno Chiarellotto

Publications and source records attributed to Bruno Chiarellotto.

14 recordsLinked to original sources

The tempered disk and the tempered cohomology

Let V be a complete discretely valued ring of mixed characteristic, with fraction field K and residue field k. Using the ind-Banach framework for derived analytic geometry, we view generic fibers of V-schemes as derived analytic spaces. This approach yields a refined notion of spectrum, richer than that of classical rigid geometry: for ex- ample we may have open subsets whose structure sheaf contains functions of logarithmic growth. In this setting, the transfer theorem for the log-growth of solutions of p-adic differ- ential equations becomes a natural continuity statement, analogous to the classical transfer theorem for radii of convergence on Berkovich spaces. Motivated by ideas of Scholze, we introduce tempered tubular neighborhoods of smooth k-schemes and define a new tempered de Rham cohomology via the derived de Rham complex of these tubes. Finally, we establish a comparison theorem showing that, for smooth proper k-schemes, tempered de Rham cohomology agrees with crystalline cohomology.

math.AG

Multivariable de Rham representations, Sen theory and $p$-adic differential equations

Let $K$ be a complete valued field extension of $\mathbf{Q}_p$ with perfect residue field. We consider $p$-adic representations of a finite product $G_{K,Δ}=G_K^Δ$ of the absolute Galois group $G_K$ of $K$. This product appears as the fundamental group of a product of diamonds. We develop the corresponding $p$-adic Hodge theory by constructing analogues of the classical period rings $\mathsf{B}_{\rm dR}$ and $\mathsf{B}_{\rm HT}$, and multivariable Sen theory. In particular, we associate to any $p$-adic representation $V$ of $G_{K,Δ}$ an integrable $p$-adic differential system in several variables $\mathsf{D}_{\rm dif}(V)$. We prove that this system is trivial if and only if the representation $V$ is de Rham. Finally, we relate this differential system to the multivariable overconvergent $(φ,Γ)$-module of $V$ constructed by Pal and Zábrádi, along classical Berger's construction.

math.NT

A Conjecture of Flach and Morin

A conjecture, recently stated by Flach and Morin, relates the action of the monodromy on the Galois invariant part of the p-adic Beilinson-Hyodo-Kato cohomology of the generic fiber of a scheme defined over a DVR of mixed characteristic to (the cohomology of) its special fiber. We prove the conjecture in the case the special fiber, of the given arithmetic scheme, is also a fiber of a geometric family over a curve in positive characteristic.

math.NT

A Hodge-Type Filtration on Rigid Cohomology

Given a scheme X over a complete discrete valuation ring ${\mathcal O}_K$ of mixed characteristic,Gros,in his study of syntomic cohomology in the smooth and proper case, introduced a filtration on the rigid cohomology of the special fiber $X_k$.Gros claimed that this construction was independent of the choice of immersions involved, citing an unpublished paper of Berthelot. However no proofs of this have appeared: here we prove it.

math.AG

Comparison of relatively unipotent log de Rham fundamental groups

In this paper, we prove compatibilities of various definitions of relatively unipotent log de Rham fundamental groups for certain proper log smooth integral morphisms of fine log schemes of characteristic zero. Our proofs are purely algebraic. As an application, we give a purely algebraic calculation of the monodromy action on the unipotent log de Rham fundamental group of a stable log curve. As a corollary we give a purely algebraic proof to the transcendental part of Andreatta-Iovita-Kim's article: obtaining in this way a complete algebraic criterion for good reduction for curves.

math.NT

Extensions of filtered Ogus structures

We compute the Ext group of the (filtered) Ogus category over a number field $K$. In particular we prove that the filtered Ogus realisation of mixed motives is not fully faithful.

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The filtered Ogus realisation of motives

We construct the (filtered) Ogus realisation of Voevodsky motives over a number field $K$. This realisation extends the functor defined on $1$-motives by Andreatta, Barbieri-Viale and Bertapelle. As an illustration we note that the analogue of the Tate conjecture holds for K3 surfaces.

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Good reduction of K3 Surfaces in equicharacteristic p

We show that for smooth and proper varieties over local fields with no non-trivial vector fields, good reduction descends over purely inseparable extensions. We use this to extend the Neron-Ogg-Shafarevich criterion for K3 surfaces to the equicharacteristic $p>0$ case.

math.AG

Around $\ell$-independence

In this article we study various forms of $\ell$-independence (including the case $\ell=p$) for the cohomology and fundamental groups of varieties over finite fields and equicharacteristic local fields. Our first result is a strong form of $\ell$-independence for the unipotent fundamental group of smooth and projective varieties over finite fields, by then proving a certain `spreading out' result we are able to deduce a much weaker form of $\ell$-independence for unipotent fundamental groups over equicharacteristic local fields, at least in the semistable case. In a similar vein, we can also use this to deduce $\ell$-independence results for the cohomology of semistable varieties from the well-known results on $\ell$-independence for smooth and proper varieties over finite fields. As another consequence of this `spreading out' result we are able to deduce the existence of a Clemens--Schmid exact sequence for formal semistable families. Finally, by deforming to characteristic $p$ we show a similar weak version of $\ell$-independence for the unipotent fundamental group of a semistable curve in mixed characteristic.

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A Néron-Ogg-Shafarevich criterion for K3 surfaces

The naive analogue of the Néron-Ogg-Shafarevich criterion is false for K3 surfaces, that is, there exist K3 surfaces over Henselian, discretely valued fields $K$, with unramified $\ell$-adic étale cohomology groups, but which do not admit good reduction over $K$. Assuming potential semi-stable reduction, we show how to correct this by proving that a K3 surface has good reduction if and only if $H^2_{\mathrm{\acute{e}t}}(X_{\overline{K}},\mathbb{Q}_\ell)$ is unramified, and the associated Galois representation over the residue field coincides with the second cohomology of a certain "canonical reduction" of $X$. We also prove the corresponding results for $p$-adic étale cohomology.

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Combinatorial degenerations of surfaces and Calabi--Yau threefolds

In this article we study combinatorial degenerations of minimal surfaces of Kodaira dimension 0 over local fields, and in particular show that the `type' of the degeneration can be read off from the monodromy operator acting on a suitable cohomology group. This can be viewed as an arithmetic analogue of results of Persson and Kulikov on degenerations of complex surfaces, and extends various particular cases studied by Matsumoto, Liedtke/Matsumoto and Hernández-Mada. We also study `maximally unipotent' degenerations of Calabi--Yau threefolds, following Kollár/Xu, showing in this case that the dual intersection graph is a 3-sphere.

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Clemens-Schmid exact sequence in characteristic p

For a semistable family of varieties over a curve in characteristic $p$, we prove the existence of a "Clemens-Schmid type" long exact sequence for the $p$-adic cohomology. The cohomology groups appearing in such a long exact sequence are defined locally

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Arithmetic and Differential Swan Conductors of rank one representations with finite local monodromy

We consider a complete discrete valuation field of characteristic p, with possibly non perfect residue field. Let V be a rank one continuous representation with finite local monodromy of its absolute Galois group. We will prove that the Arithmetic Swan conductor of V (defined after Kato in [Kat89] which fits in the more general theory of [AS02] and [AS06]) coincides with the Differential Swan conductor of the associated differential module $D^†(V)$ defined by Kedlaya in [Ked]. This construction is a generalization to the non perfect residue case of the Fontaine's formalism as presented in [Tsu98a]. Our method of proof will allow us to give a new interpretation of the Refined Swan Conductor.

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Logarithmic De Rham, Infinitesimal and Betti Cohomologies

In this article, we analyze the connection between the Log De Rham Cohomology of an fs (not necessary log smooth) log scheme $Y$ over $\mathbb C$ (for $Y$ admitting an exact closed immersion into an fs log smooth log scheme over $\mathbb C$), its Log Infinitesimal Cohomology $H^{^.}(Y^{log}_{inf}, \mathcal O_{Y^{log}_{inf}})$, and its Log Betti Cohomology, which is the Cohomology of its associated Kato-Nakayama topological space $Y^{an}_{log}$, and we prove that they are isomorphic. These results are the log scheme analogues of two classical comparison theorems.

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