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Claus Sorensen

Publications and source records attributed to Claus Sorensen.

16 recordsLinked to original sources

On the graded center of $D(G)^c$

Let $D(G)$ denote the derived category of smooth $G$-representations on $k$-vector spaces, where $G$ is a locally pro-$p$ group and $k$ is a field of characteristic $p$. In this paper we are primarily interested in the graded center of the subcategory of compact objects $Z^*(D(G)^c)$ and variants thereof. When $G$ is a $p$-adic Lie group, without proper open centralizers, we completely determine this center modulo locally nilpotent elements and give various applications.

math.NT

Projective smooth representations in natural characteristic

We investigate under which circumstances there exists nonzero {\it{projective}} smooth $\field[G]$-modules, where $\field$ is a field of characteristic $p$ and $G$ is a locally pro-$p$ group. We prove the non-existence of (non-trivial) projective objects for so-called {\it{fair}} groups -- a family including $\bf{G}(\frak{F})$ for a connected reductive group $\bf{G}$ defined over a non-archimedean local field $\frak{F}$. This was proved in \cite{SS24} for finite extensions $\frak{F}/\Bbb{Q}_p$. The argument we present in this note has the benefit of being completely elementary and, perhaps more importantly, adaptable to $\frak{F}=\Bbb{F}_q(\!(t)\!)$. Finally, we elucidate the fairness condition via a criterion in the Chabauty space of $G$.

math.NT

Derived smooth induction with applications

In natural characteristic, smooth induction from an open subgroup does not always give an exact functor. In this article we initiate a study of the right derived functors, and we give applications to the non-existence of projective representations and duality.

math.NT

Dagger groups and $p$-adic distribution algebras

Let $(G,ω)$ be a $p$-saturated group and $K/\mathbb{Q}_p$ a finite extension. In this paper we introduce the space of $K$-valued overconvergent functions $\mathcal{C}^\dagger(G,K)$. In the process we promote the rigid analytic group attached to $(G,ω)$ in a previous work of the first two authors to a dagger group. A main result of this article is that under certain assumptions (satisfied for example when $G$ is a uniform pro-$p$ group) the distribution algebra $D^\dagger(G,K)$, i.e. the strong dual of $\mathcal{C}^\dagger(G,K)$, is a Fréchet-Stein algebra in the sense of Schneider and Teitelbaum. In the last section we introduce overconvergent representations and show that there is an anti-equivalence of categories between overconvergent $G$-representations of compact type and continuous $D^\dagger(G, K)$-modules on nuclear Fréchet spaces. This is analogous to the anti-equivalence between locally analytic representations and modules over the locally analytic distribution algebra as proved by Schneider and Teitelbaum.

math.RT

dg-Hecke duality and tensor products

We continue our study of the monoidal category $D(G)$. At the level of cohomology we transfer the duality functor to the derived category of Hecke dg-modules. In the process we develop a more general and streamlined approach to the anti-involution first defined by Ollivier and Schneider. We also verify that the tensor product on $D(G)$ corresponds to an operadic tensor product on the dg-side. This uses a result of Schnürer on dg-categories with a model structure.

math.NT

Rigid vectors in $p$-adic principal series representations

In this paper we view pro-$p$ Iwahori subgroups $I$ as rigid analytic groups $\Bbb{I}$ for large enough $p$. This is done by endowing $I$ with a natural $p$-valuation, and thereby generalizing results of Lazard for $\text{GL}_n$. We work with a general connected reductive split group over some $p$-adic field (with simply connected derived group) and study the $\Bbb{I}$-analytic vectors in principal series representations. Our main result is an irreducibility criterion which generalizes results of Clozel and Ray in the $\text{GL}_n$-case.

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Duals in natural characteristic

We introduce a derived smooth duality functor on the unbounded derived category of smooth mod p representations of a p-adic Lie group. Using this functor we relate various subcategories of admissible complexes.

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Unobstructed deformation problems for GSp(4)

We prove, for many cuspidal automorphic representations for GSp(4), that the local obstructions to the deformation theory of the associated residual Galois representations generically vanish.

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A vanishing result for higher smooth duals

In this paper we prove a general vanishing result for Kohlhaase's higher smooth duality functors $S^i$. If $G$ is any unramified connected reductive $p$-adic group, $K$ is a hyperspecial subgroup, and $V$ is a Serre weight, we show that $S^i(\ind_K^G V)=0$ for $i>\dim(G/B)$ where $B$ is a Borel subgroup. (Here and throughout the paper $\dim$ refers to the dimension over $\Q_p$.) This is due to Kohlhaase for $\GL_2(\Q_p)$ in which case it has applications to the calculation of $S^i$ for supersingular representations. Our proof avoids explicit matrix computations by making use of Lazard theory, and we deduce our result from an analogous statement for graded algebras via a spectral sequence argument. The graded case essentially follows from Koszul duality between symmetric and exterior algebras.

math.NT

Koszul duality for Iwasawa algebras modulo p

In this article we establish a version of Koszul duality for filtered rings arising from $p$-adic Lie groups. Our precise setup is the following. We let $G$ be a uniform pro-$p$ group and consider its completed group algebra $Ω=k[\![G]\!]$ with coefficients in a finite field $k$ of characteristic $p$. It is known that $Ω$ carries a natural filtration and $\text{gr} Ω=S(\frak{g})$ where $\frak{g}$ is the (abelian) Lie algebra of $G$ over $k$. One of our main results in this paper is that the Koszul dual $\text{gr} Ω^!=\bigwedge \frak{g}^{\vee}$ can be promoted to an $A_{\infty}$-algebra in such a way that the derived category of pseudocompact $Ω$-modules $D(Ω)$ becomes equivalent to the derived category of strictly unital $A_{\infty}$-modules $D_{\infty}(\bigwedge \frak{g}^{\vee})$. In the case where $G$ is an abelian group we prove that the $A_{\infty}$-structure is trivial and deduce an equivalence between $D(Ω)$ and the derived category of differential graded modules over $\bigwedge \frak{g}^{\vee}$ which generalizes a result of Schneider for $\Bbb{Z}_p$.

math.NT

Functorial properties of generalised Steinberg representations

Let $G$ be the $F$-points of a connected reductive group over a non-archimedean local field $F$ of residue characteristic $p$ and $R$ be a commutative ring. Let $P=LU$ be a parabolic subgroup of $G$ and $Q$ be a parabolic subgroup of $G$ containing $P$. We study the functor $\mathrm{St}_Q^G$ taking a smooth $R$-representation $σ$ of $L$ which extends to a representation $\mathrm{e}_G(σ)$ of $G$ trivial on $U$ to the smooth $R$-representation $\mathrm{e}_G(σ) \otimes_R \mathrm{St}_Q^G(R)$ of $G$ where $\mathrm{St}_Q^G(R)$ is the generalised Steinberg representation.

math.RT

Deformation rings and parabolic induction

We study deformations of smooth mod $p$ representations (and their duals) of a $p$-adic reductive group $G$. Under some mild genericity condition, we prove that parabolic induction with respect to a parabolic subgroup $P=LN$ defines an isomorphism between the universal deformation rings of a supersingular representation $\barσ$ of $L$ and of its parabolic induction $\barπ$. As a consequence, we show that every Banach lift of $\barπ$ is induced from a unique Banach lift of $\barσ$.

math.RT

Local Langlands correspondence in rigid families

We show that local-global compatibility (at split primes) away from $p$ holds at all points of the $p$-adic eigenvariety of a definite $n$-variable unitary group. The novelty is we allow non-classical points, possibly non-étale over weight space. More precisely we interpolate the local Langlands correspondence for GL(n) across the eigenvariety by considering the fibers of its defining coherent sheaf. We employ techniques of Scholze from his new approach to the local Langlands conjecture.

math.NT

Strong local-global compatibility in the p-adic Langlands program for U(2)

We prove that certain Galois-isotypic parts of the completed cohomology group for U(2) can be written as a completed tensor product of a representation coming from the p-adic Langlands correspondence for $GL_2(\mathbb{Q}_p)$ and a representation arising via the local Langlands correspondence in famillies of Emerton and Helm.

math.NT

The local Langlands correspondence in families and Ihara's lemma for U(n)

The goal of this paper is to reformulate the conjectural "Ihara lemma" for $U(n)$ in terms of the local Langlands correspondence in families $\tildeπ_Σ(\cdot)$, as currently being developed by Emerton and Helm. The reformulation roughly takes the following form. Suppose we are given an irreducible mod $\ell$ Galois representation $\bar{r}$, which is modular of full level (and small weight), and a finite set of places $Σ$ -- none of which divide $\ell$. Then $\tildeπ_Σ(r)$ exists, and has a global realization as a natural module of algebraic modular forms, where $r$ is the universal $Σ$-deformation of $\bar{r}$. This is unconditional for $n=2$, where Ihara's lemma is an almost trivial consequence of the strong approximation theorem.

math.NT

Weak local-global compatibility in the p-adic Langlands program for U(2)

Inspired by Emerton's work for GL(2), we study the completed cohomology of the tower of finite sets associated with a definite unitary group in two variables. When p splits (and other technical assumptions are fulfilled), we show that the p-adic local Langlands correspondence for GL(2) (over Q_p) occurs in the cohomology. We give an application to the Fontaine-Mazur conjecture over CM fields.

math.NT