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Nadir Matringe

Publications and source records attributed to Nadir Matringe.

At least 37 records · Page 2Linked to original sources
arXiv2022

Whittaker functionals and contragredient in characteristic not $p$

Let $R$ be an algebraically closed field and $\ell$ be its characteristic. Let $G$ be a locally profinite group having a compact open subgroup of invertible pro-order in $R$. Take $N$ a closed subgroup of $G$ exhausted by compact subgroups of invertible pro-orders in $R$ and fix a smooth character $θ$ of $N$. For $π$ an irreducible smooth $R$-representation of $G$ whose matrix coefficients are compactly supported modulo the center (we call it $Z$-compact), we show that the dimensions $\mathrm{Hom}_{N}(π,θ)$ and $\mathrm{Hom}_{N}(π^\vee,θ^{-1})$ are equal provided one of the two is finite. We derive a few applications from this result. First, we prove that any $G$-intertwiner from $π$ to $\mathrm{Ind}_N^G(θ)$ has image in $\mathrm{ind}_{ZN}^G(ω_πθ)$, where $ω_π$ is the central character of $π$, and the Whittaker space of $π$ agrees with that of its Whittaker periods. Second, it applies to quasi-split groups over non Archimedean local fields of residual characteristic $p \neq \ell$ and where $N$ is the unipotent radical of a Borel subgroup of $G$ together with a generic character $θ$. Our equality of dimensions turns out to be a good replacement for Rodier's crucial use of complex conjugation in the proof of Whittaker multiplicity at most one for cuspidal representations. Then by a lifting argument, we recover Rodier's generalization of the Gelfand-Kazhdan property for $R$-valued $(θ^{-1}\otimes θ)$-equivariant distributions on $G$. This latter fact, together with Rodier's heridity property, which is valid in our context, leads to the multiplicity at most one of Whittaker functionals over $R$. We also give other applications, including a generalization over $R$ of a result for complex representations proved by Chang Yang and initially conjectured by Dipendra Prasad.

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arXiv2022

Local distinction, quadratic base change and automorphic induction for $\mathrm{GL_n}$

Behind this sophisticated title hides an elementary exercise on Clifford theory for index two subgroups and self-dual/conjugate-dual representations. When applied to semi-simple representations of the Weil-Deligne group $W'_F$ of a non Archimedean local field $F$, and further translated in terms of representations of $\mathrm{GL_n}(F)$ via the local Langlands correspondence when $F$ has characteristic zero, it yields various statements concerning the behaviour of different types of distinction under quadratic base change and automorphic induction. When $F$ has residual characteristic different from $2$, combining of one of the simple results that we obtain with the tiviality of conjugate-orthogonal root numbers (proved by Gan, Gross and Prasad), we recover without using the LLC a result of Serre on the parity of the Artin conductor of orthogonal representations of $W'_F$. On the other hand we discuss its parity for symplectic representations using the LLC and the Prasad and Takloo-Bighash conjecture.

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arXiv2022

Intertwining periods and distinction for p-adic Galois symmetric pairs

We consider distinction of representations in the context of $p$-adic Galois symmetric spaces. We provide new sufficient conditions for distinction of parabolically induced representations in terms of similar conditions on the inducing data and deduce a characterization for distinction of representations parabolically induced from cuspidal. We explicate the results further for classical groups and give several applications, in particular, concerning the preservation of distinction via Langlands functoriality. We relate our results with a conjecture of Dipendra Prasad.

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arXiv2022

The Kirillov model in families

Let $F$ be a non-archimedean local field, let $k$ be an algebraically closed field of characteristic $\ell$ different from the residual characteristic of $F$, and let $A$ be a commutative Noetherian $W(k)$-algebra, where $W(k)$ denotes the Witt vectors. Using the Rankin-Selberg functional equations and extending recent results of the second author, we show that if $V$ is an $A[\text{GL}_n(F)]$-module of Whittaker type, then the mirabolic restriction map on its Whittaker space is injective. This gives a new quick proof of the existence of Kirillov models for representations of Whittaker type, including complex representations, which generalizes to the $\ell$-modular and families setting, in contrast with the previous proofs. In the special case where $A=k=\overline{\mathbb{F}_{\ell}}$ and $V$ is irreducible generic, our result in particular answers a question of Vignéras from 1989.

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arXiv2021

Gamma factors of intertwining periods and distinction for inner forms of $\mathrm{GL(n)}$

Let $F$ be a $p$-adic field, $E$ be a quadratic extension of $F$, $D$ be an $F$-central division algebra of odd index and let $θ$ be the Galois involution attached to $E/F$. Set $H=GL(m,D)$, $G=GL(m,D\otimes_F E)$, and let $P=MU$ be a standard parabolic subgroup of $G$. Let $w$ be a Weyl involution stabilizing $M$ and $M^{θ_w}$ be the subgroup of $M$ fixed by the involution $θ_w:m\mapsto θ(wmw)$. We denote by $X(M)^{w,-}$ the complex torus of $w$-anti-invariant unramified characters of $M$. Following the global methods of Jacquet, Lapid and Rogawski, we associate to a finite length representation $σ$ of $M$ and to a linear form $L\in Hom_{M^{θ_w}}(σ,\mathbb{C})$ a family of $H$-invariant linear forms called intertwining periods on $Ind_P^G(χσ)$ for $χ\in X(M)^{w,-}$, which is meromorphic in the variable $χ$. Then we give sufficient conditions for some of these intertwining periods, namely the open intertwining periods studied by Blanc and Delorme, to have singularities. By a local/global method, we also compute in terms of Asai gamma factors the proportionality constants involved in their functional equations with respect to certain intertwining operators. As a consequence, we classify distinguished unitary and ladder representations of $G$, extending respectively results the author and Gurevich for $D=F$, which both relied at some crucial step on the theory of Bernstein-Zelevinsky derivatives. We make use of one of a recent result of Beuzart-Plessis which in the case of the group $G$ asserts that the Jacquet-Langlands correspondence preserves distinction. Such a result is for essentially square-integrable representations, but our method in fact allows us to use it only for cuspidal representations of $G$.

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arXiv2020

Some questions on global distinction for $\mathrm{SL}(n)$

Let $E/F$ be a quadratic extension of number fields and let $π$ be an $\mathrm{SL}_n(\mathbb{A}_F)$-distinguished cuspidal automorphic representation of $\mathrm{SL}_n(\mathbb{A}_E)$. Using an unfolding argument, we prove that an element of the $\mathrm{L}$-packet of $π$ is distinguished if and only if it is $ψ$-generic for a non-degenerate character $ψ$ of $N_n(\mathbb{A}_E)$ trivial on $N_n(E+\mathbb{A}_F)$, where $N_n$ is the group of unipotent upper triangular matrices of $\mathrm{SL}_n$. We then use this result to analyze the non-vanishing of the period integral on different realizations of a distinguished cuspidal automorphic representation of $\mathrm{SL}_n(\mathbb{A}_E)$ with multiplicity $> 1$, and show that in general some canonical copies of a distinguished representation inside different $\mathrm{L}$-packets can have vanishing period. We also construct examples of everywhere locally distinguished representations of $\mathrm{SL}_n(\mathbb{A}_E)$ the $\mathrm{L}$-packets of which do not contain any distinguished representation.

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arXiv2020

Distinction inside L-packets of SL(n)

If $E/F$ is a quadratic extension $p$-adic fields, we first prove that the $\mathrm{SL}_n(F)$-distinguished representations inside a distinguished unitary L-packet of $\mathrm{SL}_n(E)$ are precisely those admitting a degenerate Whittaker model with respect to a degenerate character of $N(E)/N(F)$. Then we establish a global analogue of this result. For this, let $E/F$ be a quadratic extension of number fields and let $π$ be an $\mathrm{SL}_n(\mathbb{A}_F)$-distinguished square integrable automorphic representation of $\mathrm{SL}_n(\mathbb{A}_E)$. Let $(σ,d)$ be the unique pair associated to $π$, where $σ$ is a cuspidal representation of $\mathrm{GL}_r(\mathbb{A}_E)$ with $n=dr$. Using an unfolding argument, we prove that an element of the L-packet of $π$ is distinguished with respect to $\mathrm{SL}_n(\mathbb{A}_F)$ if and only if it has a degenerate Whittaker model for a degenerate character $ψ$ of type $r^d:=(r,\dots,r)$ of $N_n(\mathbb{A}_E)$ which is trivial on $N_n(E+\mathbb{A}_F)$, where $N_n$ is the group of unipotent upper triangular matrices of $\mathrm{SL}_n$. As a first application, under the assumptions that $E/F$ splits at infinity and $r$ is odd, we establish a local-global principle for $\mathrm{SL}_n(\mathbb{A}_F)$-distinction inside the L-packet of $π$. As a second application we construct examples of distinguished cuspidal automorphic representations $π$ of $\mathrm{SL}_n(\mathbb{A}_E)$ such that the period integral vanishes on some canonical copy of $π$, and of everywhere locally distinguished representations of $\mathrm{SL}_n(\mathbb{A}_E)$ such that their L-packets do not contain any distinguished representation.

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arXiv2020

The split case of the Prasad--Takloo-Bighash conjecture for cuspidal representations of level zero

Let $E/F$ be a quadratic extension of non archimedean local fields of odd residual characteristic. We prove a conjecture of Prasad and Takloo-Bighash, in the case of cuspidal representations of depth zero of $\mathrm{GL}(2m,F)$. This conjecture characterizes distinction for the pair $(\mathrm{GL}(2m,F),\mathrm{GL}(m,E))$ with respect to a character $μ\circ \mathrm{det}$ of $\mathrm{GL}(m,E)$, in terms of certain conditions on Langlands paremeters, including an epsilon value. We also compute the multiplicity of the involved equivariant linear forms when $E/F$ is unramified, and also when $μ$ is tame. In both cases this multiplicity is at most one.

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arXiv2019

A characterization of the relation between two $\ell$-modular correspondences

Let $F$ be a non archimedean local field of residual characteristic $p$ and $\ell$ a prime number different from $p$. Let $\mathrm{V}$ denote Vignéras' $\ell$-modular local Langlands correspondence between irreducible $\ell$-modular representations of $\mathrm{GL}_n(F)$ and $n$-dimensional $\ell$-modular Deligne representations of the Weil group $\mathrm{W}_F$. In a previous work, enlarging the space of parameters to Deligne representations with non necessarily nilpotent operators, we proposed a modification of the correspondence of Vignéras into a correspondence $\mathrm{C}$ compatible with the formation of local constants in the generic case. In this note, following a remark of Alberto Mínguez, we characterize the modification $\mathrm{C}\circ \mathrm{V}^{-1}$ by a short list of natural properties.

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arXiv2019

Test vectors for finite periods and base change

Let $E/F$ be a quadratic extension of finite fields. By a result of Gow, an irreducible representation $π$ of $G = {\rm GL}_n(E)$ has at most one non-zero $H$-invariant vector, up to multiplication by scalars, when $H$ is ${\rm GL}_n(F)$ or ${\rm U}(n,E/F)$. If $π$ does have an $H$-invariant vector it is said to be $H$-distinguished. It is known, from the work of Gow, that $H$-distinction is characterized by base change from ${\rm U}(n,E/F)$, due to Kawanaka, when $H$ is ${\rm GL}_n(F)$ (resp. from ${\rm GL}_n(F)$, due to Shintani, when $H$ is ${\rm U}(n,E/F)$). Assuming $π$ is generic and $H$-distinguished, we give an explicit description of the $H$-invariant vector in terms of the Bessel function of $π$. Let $ψ$ be a non-degenerate character of $N_G/N_H$ and let $B_{π,ψ}$ be the (normalized) Bessel function of $π$ on the $ψ$-Whittaker model. For the $H$-average \[W_{π,ψ} = \frac{1}{|H|} \sum_{h\in H} π(h) B_{π,ψ}\] of the Bessel function, we prove that \[W_{π,ψ}(I_n) = \frac{{\rm dim}ρ}{{\rm dim} π} \cdot \frac{|{\rm GL}_n(E)|}{|{\rm GL}_n(F)| |{\rm U}(n,E/F)|},\] where $ρ$ is the representation of ${\rm U}(n,E/F)$ (resp. ${\rm GL}_n(F)$) that base changes to $π$ when $H$ is ${\rm GL}_n(F)$ (resp. ${\rm U}(n,E/F)$). As an application we classify the members of a generic $L$-packet of ${\rm SL}_n(E)$ that admit invariant vectors for ${\rm SL}_n(F)$. Finally we prove a $p$-adic analogue of our result for square-integrable representations in terms of formal degrees by employing the formal degree conjecture of Hiraga-Ichino-Ikeda \cite{hii08}.

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arXiv2019

Multiplicity one for pairs of Prasad--Takloo-Bighash type

Let $E/F$ be a quadratic extension of non-archimedean local fields of characteristic different from $2$. Let $A$ be an $F$-central simple algebra of even dimension so that it contains $E$ as a subfield, set $G=A^\times$ and $H$ for the centralizer of $E^\times$ in $G$. Using a Galois descent argument, we prove that all double cosets $H g H\subset G$ are stable under the anti-involution $g\mapsto g^{-1}$, reducing to Guo's result for $F$-split $G$ which we extend to fields of positive characteristic different from $2$. We then show, combining global and local results, that $H$-distinguished irreducible representations of $G$ are self-dual and this implies that $(G,H)$ is a Gelfand pair: \[dim_{\mathbb{C}}(Hom_{H}(π,\mathbb{C}))\leq 1\] for all smooth irreducible representations $π$ of $G$. Finally we explain how to obtain the the multiplicity one statement in the archimedean case using the criteria of Aizenbud and Gourevitch, and we then show self-duality of irreducible distinguished representations in the archimedean case too.

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arXiv2019

Galois self-dual cuspidal types and Asai local factors

Let $F/F_{\mathsf{o}}$ be a quadratic extension of non-archimedean locally compact fields of odd residual characteristic and $σ$ be its non-trivial automorphism. We show that any $σ$-self-dual cuspidal representation of ${\rm GL}_n(F)$ contains a $σ$-self-dual Bushnell--Kutzko type. Using such a type, we construct an explicit test vector for Flicker's local Asai $L$-function of a ${\rm GL}_n(F_{\mathsf{o}})$-distinguished cuspidal representation and compute the associated Asai root number. Finally, by using global methods, we compare this root number to Langlands--Shahidi's local Asai root number, and more generally we compare the corresponding epsilon factors for any cuspidal representation.

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arXiv2019

Characterisation of the poles of the $\ell$-modular Asai $L$-factor

Let $E/F$ be a quadratic extension of non-archimedean local fields, and let $\ell$ be a prime number different from the residual characteristic of $F$. For a complex cuspidal representation $π$ of $GL(n,E)$, the Asai $L$-factor $L^+(X,π)$ has a pole at $X=1$ if and only if $π$ is $GL(n,F)$-distinguished. In this paper we solve the problem of characterising the occurrence of a pole at $X=1$ of $L^+(X,π)$ when $π$ is an $\ell$-modular cuspidal representation of $GL(n,E)$: we show that $L^+(X,π)$ has a pole at $X=1$ if and only if $π$ is a relatively banal distinguished representation; namely $π$ is $GL(n,F)$-distinguished but not $\vert\det(~ )|_{F}$-distinguished. This notion turns out to be an exact analogue for the symmetric space $GL(n,E)/GL(n,F)$ of M\' inguez and Sécherre's notion of banal cuspidal $\overline{\mathbb{F}}_\ell$-representation of $GL(n,F)$. Along the way we compute the Asai $L$-factor of all cuspidal $\ell$-modular representations of $GL(n,E)$ in terms of type theory, and prove new results concerning lifting and reduction modulo $\ell$ of distinguished cuspidal representations. Finally, we determine when the natural $GL(n,F)$-period on the Whittaker model of a distinguished cuspidal representation of $GL(n,E)$ is nonzero.

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arXiv2018

Linear and Shalika local periods for the mirabolic group, and some consequences

Using linear periods on the mirabolic subgroup of $GL(n,F)$, for $F$ a non archimedean local field, we give a list of the maximal Levi subgroups of $GL(n,F)$ which can distinguish a discrete series, and a generic representation. We also obtain the functional equation of the local exterior-square $L$-function of a generic representation of $GL(n,F)$ when $n=2m$ is even. Then we discuss the relation between Shalika models and local models for representations of $GL(2m,F)$. Finally we give a necessary and sufficient condition on the cuspidal representation $ρ$ for a generalised Steinberg representation $St_k(ρ)$ of $GL(2m,F)$ to have a local model.

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arXiv2018

Extension of Whittaker functions and test vectors

We show that certain products of Whittaker functions and Schwartz functions on a general linear group extend to Whittaker functions on a larger general linear group. This generalizes results of Cogdell--Piatetski-Shapiro \cite{CPS} and Jacquet--Piatetski-Shapiro--Shalika \cite{JPSS83}. As a consequence, we prove that the Rankin--Selberg $L$-factor of the product of a discrete series representation and the Zelevinsky dual of a discrete series representation is given by a single Rankin--Selberg integral.

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arXiv2018

The $\ell$-modular local Langlands correspondence and local factors

Let $F$ be a non-archimedean local field of residual characteristic $p$, $\ell\neq p$ be a prime number, and $\mathrm{W}_F$ the Weil group of $F$. We classify the indecomposable $\mathrm{W}_F$-semisimple Deligne $\overline{\mathbb{F}_\ell}$-representations in terms of the irreducible $\overline{\mathbb{F}_\ell}$-representations of $\mathrm{W}_F$, and extend constructions of Artin-Deligne local factors to this setting. Finally, we define a variant of the $\ell$-modular local Langlands correspondence which satisfies a preservation of local factors statement for generic representations.

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arXiv2017

Test vectors for local cuspidal Rankin-Selberg integrals of GL(n), and reduction modulo $\ell$

Let $π_1,π_2$ be a pair of cuspidal complex, or $\ell$-adic, representations of the general linear group of rank $n$ over a non-archimedean local field $F$ of residual characteristic $p$, different to $\ell$. Whenever the local Rankin-Selberg $L$-factor $L(X,π_1,π_2)$ is nontrivial, we exhibit explicit test vectors in the Whittaker models of $π_1$ and $π_2$ such that the local Rankin-Selberg integral associated to these vectors and to the characteristic function of $\mathfrak{o}_F^n$ is equal to $L(X,π_1,π_2)$. We give an initial application of the test vectors to reduction modulo $\ell$ of $\ell$-adic $L$-factors.

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