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Arno Kret

Publications and source records attributed to Arno Kret.

12 recordsLinked to original sources
arXiv2026

Invariance Galoisienne des z\'eros centraux de fonctions L

Nous d\'emontrons l'invariance Galoisienne de la propri\'et\'e d'annulation en $1/2$ des fonctions L standard ou de Rankin-Selberg pour certaines repr\'esentations automorphes cuspidales alg\'ebriques r\'eguli\`eres autoduales ou autoduales conjugu\'ees de groupes lin\'eaires sur un corps de nombres arbitraire. La d\'emonstration repose sur l'utilisation de la cohomologie pond\'er\'ee de Goresky-Harder-MacPherson et sur la construction de certaines repr\'esentations automorphes discr\`etes pour les groupes classiques comme r\'esidus de s\'eries d'Eisenstein. L'abandon de l'hypoth\`ese ``$F$ totalement r\'eel'' introduit de nouvelles difficult\'es concernant certains op\'erateurs d'entrelacement. Celles-ci sont r\'esolues gr\^ace \`a l'appendice, r\'edig\'e par J.-L. Waldspurger et l'un d'entre nous, d\'emontrant l'holomorphie et la non-annulation de certains op\'erateurs d'entrelacement normalis\'es. Nous d\'emontrons \'egalement l'invariance Galoisienne des facteurs epsilon correspondants, impliquant l'invariance Galoisienne de la parit\'e de l'ordre d'annulation en $1/2$ de ces fonctions $L$. -- We prove the invariance under the Galois group of the vanishing at $1/2$ of standard and Rankin-Selberg L-functions for certain self-dual or conjugate self-dual algebraic cuspidal automorphic representations for general linear groups over an arbitrary number field. The proof uses Goresky-Harder-MacPherson weighted cohomology and the construction of certain discrete automorphic representations for classical groups as residues of Eisenstein series. New difficulties appear concerning certain intertwining operators. These are solved in the appendix by J.-L. Waldspurger and O. Ta\"ibi proving the holomorphy and non-vanishing of these operators. We also prove the Galois invariance of epsilon factors, implying Galois invariance of the parity of the order at $1/2$ of L-functions.

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arXiv2023

Integral points on coarse Hilbert moduli schemes

We continue our study of integral points on moduli schemes by combining the method of Faltings (Arakelov, Parsin, Szpiro) with modularity results and Masser-Wüstholz isogeny estimates. In this work we explicitly bound the height and the number of integral points on coarse Hilbert moduli schemes outside the branch locus. In the first part we define and study coarse Hilbert moduli schemes with their heights and branch loci. In the second part we establish the effective Shafarevich conjecture for abelian varieties $A$ over a number field $K$ such that $A_{\bar{K}}$ has CM or $A_{\bar{K}}$ is of GL2-type and isogenous to all its $G_\mathbb Q$-conjugates. In the third part we continue our explicit study of the Parsin construction given by the forgetful morphism of Hilbert moduli schemes. We now work out our strategy for arbitrary number fields $K$ and we explicitly bound the number of polarizations and module structures on abelian varieties over $K$ with real multiplications. In the last part we illustrate our results by applying them to two classical surfaces first studied by Clebsch (1871) and Klein (1873): We explicitly bound the Weil height and the number of their integral points.

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arXiv2023

On the central value of Rankin $L$-functions for self-dual algebraic representations of linear groups over totally real fields

Deligne has formulated extremely influential conjectures about certain special values of the $L$-functions of (Grothendieck) motives over a number field $F$. Given the conjectural dictionary between motives and 'algebraic' automorphic representations of $\textrm{GL}(N, {\mathbb A}_F)$, where ${\mathbb A}_F$ denotes the ad\`eles of $F$, they translate into conjectures concerning the $L$-functions of these automorphic representations. These complex representations, when they are 'regular', can be conjugated by the automorphisms of the complex field ${\mathbb C}$. It then follows, as a weak consequence of Deligne's conjectures, that the vanishing at critical points (integers of half-integers) of the automorphic $L$-functions should be invariant by automorphisms of ${\mathbb C}$. If $F$ is totally imaginary, this has been proven by Moeglin, for standard or Rankin $L$-functions. Here we extend the result to Rankin $L$-fuctions for totally real fields $F$, under a parity and a regularity assumption. The proof relies on Eisenstein cohomology and the Zucker conjecture (a theorem of Looijenga and Saper-Stern.)

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arXiv2022

Galois representations for even general special orthogonal groups

We prove the existence of $\mathrm{GSpin}_{2n}$-valued Galois representations corresponding to cohomological cuspidal automorphic representations of certain quasi-split forms of $\mathrm{GSO}_{2n}$ under the local hypotheses that there is a Steinberg component and that the archimedean parameters are regular for the standard representation. This is based on the cohomology of Shimura varieties of abelian type, of type $D^{\mathbb{H}}$, arising from forms of $\mathrm{GSO}_{2n}$. As an application, under similar hypotheses, we compute automorphic multiplicities, prove meromorphic continuation of (half) spin $L$-functions, and improve on the construction of $\mathrm{SO}_{2n}$-valued Galois representations by removing the outer automorphism ambiguity.

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arXiv2022

Galois representations for general symplectic groups

We prove the existence of GSpin-valued Galois representations corresponding to cohomological cuspidal automorphic representations of general symplectic groups over totally real number fields under the local hypothesis that there is a Steinberg component. This confirms the Buzzard-Gee conjecture on the global Langlands correspondence in new cases. As an application we complete the argument by Gross and Savin to construct a rank seven motive whose Galois group is of type G_2 in the cohomology of Siegel modular varieties of genus three. Under some additional local hypotheses we also show automorphic multiplicity one as well as meromorphic continuation of the spin L-functions.

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arXiv2021

$H^0$ of Igusa varieties via automorphic forms

Our main theorem describes the degree 0 cohomology of Igusa varieties in terms of one-dimensional automorphic representations in the setup of mod p Hodge-type Shimura varieties with hyperspecial level at p, mirroring the well known analogue for complex Shimura varieties. As an application, we obtain a completely new approach to two geometric questions. (See Sect. 1.5 for a comparison with independent results by van Hoften and Xiao via a different approach.) Firstly, we verify the discrete part of the Hecke orbit conjecture, which amounts to irreducibility of central leaves, generalizing preceding works by Chai, Oort, Yu, et al. Secondly, we deduce irreducibility of Igusa towers and its generalization to non-basic Igusa varieties in the same generality, extending previous results by Igusa, Ribet, Faltings--Chai, Hida, and others. Our proof is based on a Langlands--Kottwitz-type formula for Igusa varieties due to Mack-Crane, an asymptotic study of the trace formula, and an estimate for unitary representations and their Jacquet modules in representation theory of $p$-adic groups due to Howe--Moore and Casselman.

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arXiv2019

Integral points on Hilbert moduli schemes

We use the method of Faltings (Arakelov, Paršin, Szpiro) in order to explicitly study integral points on a class of varieties over $\mathbb Z$ called Hilbert moduli schemes. For instance, integral models of Hilbert modular varieties are classical examples of Hilbert moduli schemes. Our main result gives explicit upper bounds for the height and the number of integral points on Hilbert moduli schemes.

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arXiv2013

The trace formula and the existence of PEL type Abelian varieties modulo p

We show, using the trace formula, that any Newton stratum of a Shimura variety of PEL-type of types (A) and (C) is non-empty at the primes of good reduction. Furthermore we prove conditionally the non-emptiness for Shimura data associated to odd Spin groups. Our results are conditional on Rapoport-Langlands conjecture and Arthur's conjectures on the discrete spectrum. Both these results have been announced by Arthur and Kisin in significant cases.

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arXiv2013

Equidistribution in supersingular Hecke orbits

We prove an equidistribution result for Hecke operators acting on the basic stratum of certain Shimura varieties. We relate the rate of convergence to the bounds from the Ramanujan conjecture of certain cuspidal automorphic representations on Gl_n for which this conjecture is known, and therefore we obtain optimal estimates on the rate of convergence.

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arXiv2012

Combinatorics of the basic stratum

We express the cohomology of the basic stratum of some unitary Shimura varieties associated to division algebras in terms of automorphic representations of the group in the Shimura datum.

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arXiv2012

The basic stratum of some simple Shimura varieties

Under simplifying hypotheses we prove a relation between the l-adic cohomology of the basic stratum of a Shimura variety of PEL-type modulo a prime of good reduction of the reflex field and the cohomology of the complex Shimura variety. In particular we obtain explicit formulas for the number of points in the basic stratum over finite fields. We obtain our results using the trace formula and truncation of the formula of Kottwitz for the number of points on a Shimura variety over a finite fields.

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