arXiv subjects
Christophe Cornut
Publications and source records attributed to Christophe Cornut.
Morphing etale spaces
We give a simple description of the category of sheaves on the small etale site of an irreducible scheme whose local rings are geometrically unibranch and henselian, which affords a characterization of representable sheaves.
On triangles with a minuscule side
Let $W\subset O(V)$ be the Weyl group of a root system $R\subset V$. If $a+b+c=0=a'+b'+c'$ with $a$, $b$ and $c$ respectively conjugated to $a'$, $b'$ and $c'$ in V , then $(a,b,c)$ is conjugated to $(a',b',c')$ in $V^3$ when each projection of $a$ to an irreducible component of $V$ is co-linear to a minuscule coweight.
On Harder-Narasimhan filtrations and their compatibility with tensor products
We attach buildings to modular lattices and use them to develop a metric approach to Harder-Narasimhan filtrations. Switching back to a categorical framework, we establish an abstract numerical criterion for the compatibility of these filtrations with tensor products. We finally verify our criterion in three cases, one of which is new.
Mazur's inequality and laffaille's theorem
We look at various questions related to filtrations in $p$-adic Hodgetheory, using a blend of building and Tannakian tools. Specifically,Fontaine and Rapoport used a theorem of Laffaille on filtered isocrystalsto establish a converse of Mazur's inequality for isocrystals. Wegeneralize both results to the setting of (filtered) $G$-isocrystalsand also establish an analog of Totaro's $\otimes$-product theoremfor the Harder-Narasimhan filtration of Fargues.
Filtrations and Buildings
We construct and study a scheme theoretical version of the Tits vectorial building, relate it to filtrations on fiber functors, and use them to clarify various constructions pertaining to Bruhat-Tits buildings, for which we also provide a Tannakian description.
Harder-Narasimhan filtrations for Breuil-Kisin-Fargues modules
We define and study Harder-Narasimhan filtrations on Breuil-Kisin-Fargues modules and related objects relevant to p-adic Hodge theory.
Generators of the pro-p Iwahori and Galois representations
For an odd prime p, we determine a minimal set of topological generators of the pro-p Iwahori subgroup of a split reductive group G over Z\_p. In the simple adjoint case and for any sufficiently large regular prime p, we also construct Galois extensions of Q with Galois group between the pro-p and the standard Iwahori subgroups of G.
Cristaux et immeubles
Let G be a connected reductive group defined over Q_p. The set of crystals contained in a given G-isocrystal is viewed from a Bruhat-Tits building-theoretic vantage point as a kind of tubular neighborhood of a skeleton characterized by a minimality property arising from metric space theory.
Liftings of Reduction Maps for Quaternion Algebras
We construct liftings of reduction maps from CM points to supersingular points for general quaternion algebras and use these liftings to establish a precise correspondence between CM points on indefinite quaternion algebras with a given conductor and CM points on certain corresponding totally definite quaternion algebras.