Victor Ostrik
In this note we show that all reductive groups are clean in odd characteristic. In characteristic 2 there are two cuspidal local systems (one for $F_4$ and one for $E_8$) which can not be handled by our method.
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Let $F$ be a non-archimedean local field of residue characteristic $p$, $G$ be the group $GL(n, F)$. In this note, under the assumption $(n, p)=1$, we show a simple cuspidal representation $π$ (that with normalized level $\frac{1}{n}$) of $G$ is determined uniquely up to isomorphism by the local constants of $χ\circ \text{det}\otimes π$ for all characters $χ$ of $F^\times$.
We prove a strong induction theorem for graded Hecke algebras and we classify the tempered and square integrable representations of such algebras using methods of equivariant homology.
Let $ρ$ is a cuspidal representation of $GL(n,F)$, with $F$ a non archimedean local field, and $H$ a maximal Levi subgroup of $GL(n,F)$. We show that if $ρ$ is $H$-distinguished, then $n$ is even, and $H\simeq GL(n/2,F)\times GL(n/2,F)$.
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 num…
We prove that any reductive group G over a non-Archimedean local field has a cuspidal complex representation.
We construct an endoscopic decomposition for local L-packets associated to irreducible cuspidal Deligne-Lusztig representations. Moreover, the obtained decomposition is compatible with inner twistings.
Let $G_n$ denote either the group $Sp(2n, F)$ or $SO(2n+1, F)$ over a non-archimedean local field $F$. We determine the composition series of representations of $G_n$ induced from cuspidal and ladder representations such that the minimal exponent in the cuspidal support of the ladder representation is greater than or equal to $\frac{1}{2}$.
For a classical group over a non-archimedean local field of odd residual characteristic p, we construct all cuspidal representations over an arbitrary algebraically closed field of characteristic different from p, as representations induced from a cuspidal type. We also give a fundamental step towards the classification of cuspidal representations, identifying when certain cuspidal types induce to equivalent representations; this result is new even in the case of complex representations. Finally, we prove that the representations induced from more general types are quasi-projective, a crucial …
We show how the modular representation theory of inner forms of general linear groups over a non-Archimedean local field can be brought to bear on the complex theory in a remarkable way. Let F be a non-Archimedean locally compact field of residue characteristic p, and let G be an inner form of the general linear group GL(n,F). We consider the problem of describing explicitly the local Jacquet--Langlands correspondence between the complex discrete series representations of G and GL(n,F), in terms of type theory. We show that the congruence properties of the local Jacquet--Langlands corresponden…
On some non-principal locally analytic representations induced by cuspidal Lie algebra representations
本文研究了由cuspidal李代数表示诱导的非主次局部解析表示的构造与性质，证明了其ind-admissible性及超cuspidal性，并在特定情况下证明了拓扑不可约性。
Theta representations appear globally as the residues of Eisenstein series on covers of groups; their unramified local constituents may be characterized as subquotients of certain principal series. A cuspidal theta representation is one which is equal to the local twisted theta representation at almost all places. Cuspidal theta representations are known to exist but only for covers of $GL_j$, $j\leq 3$. In this paper we establish necessary conditions for the existence of cuspidal theta representations on the $r$-fold metaplectic cover of the general linear group of arbitrary rank.
This paper proves the existence of cuspidal automorphic forms for a reductive group, invariant under an automorphism of finite order. The techniques used are a local analysis of orbital integrals and the Arthur-Selberg trace formula.
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 $\…
In this paper we give a simple (local) proof of two principal results about irreducible tempered representations of general linear groups over a non-archimedean local division algebra. We give a proof of the parameterization of the irreducible square integrable representations of these groups by segments of cuspidal representations, and a proof of the irreducibility of the tempered parabolic induction. Our proofs are based on Jacquet modules (and the Geometric Lemma, incorporated in the structure of a Hopf algebra). We use only some very basic general facts of the representation theory of redu…
Cuspidal $\ell$-modular representations of $\mathrm{GL}_n(F)$ distinguished by a Galois involution
本文研究局部域二次扩张下由Galois对合区分的GL_n的尖点l-模表示，将分类归约为level 0情形，给出σ-自对偶表示被区分的必要条件，并分类了具有到Q_l的区分尖点提升的F_l-表示。
In this paper we prove the following conditional result: Let F be a number field, and pi a cusp form on GL(2)/F which is not solvable polyhedral. Assume that all the symmetric powers sym^m(pi) are modular, i.e., define automorphic forms on GL(m+1)/F. If sym^6(pi) is cuspidal, then all the symmetric powers are cuspidal, for all m. Moreover, sym^6(pi) is Eisenteinian iff sym^5(pi) is an abelian twist of the functorial product of pi with the symmetric square of a cusp form pi' on GL(2)/F.
Let $F$ be any non-Archimedean local field with a Galois involution $σ$ and $F_0$ be the fixed field for the action of $σ$. When the residue characteristic of $F_0$ is odd, using the explicit construction of cuspidal representations of classical groups by Stevens, we classify generic cuspidal representations of $U(2,1)(F/F_0)$.
Orbital integral bounds the character for cuspidal representations of $GL_n(\mathbb{F}_{\ell}((t)))$
本文证明了 $GL_n(\mathbb{F}_{\ell}((t)))$ 的 cuspidal 表示特征由轨道积分限制，为正特征下哈里-沙德拉积分可积定理的证明提供了基础。
Exterior square gamma factors for cuspidal representations of $\mathrm{GL}_n$: simple supercuspidal representations
本文计算了简单超尖点表示的局部扭曲外平方 gamma 因子，并据此证明了该类表示的局部逆定理。
Let $\mathbf{G}$ be an unramified quasi-split unitary group over a p-adic field of odd residual characteristic. The goal of this paper is to describe the supercuspidal representations within certain L-packets of $\mathbf{G}$, which are classified by Arthur and Mok using the theory of endoscopy. The description is given in terms of the cuspidal types constructed by Bushnell-Kutzko and Stevens. As a starting example, we require the parameters of our packets to satisfy certain regularity conditions, such that these packets consist of very cuspidal representations in the sense of Adler and Reeder.…
Cuspidal endo-support and strong beta extensions
本文研究了在非阿基米德局部域上，一般线性群或经典群的内形式G的光滑表示的极小内支撑及强贝塔扩展，探讨了其与 cuspidal 支持的关系，并用于分解光滑R-表示范畴。
Let $G$ be a symplectic group over a nonarchimedean local field of characteristic zero and odd residual characteristic. Given an irreducible cuspidal representation of G, we determine its Langlands parameter (equivalently, its Jordan blocks in the language of Moeglin) in terms of the local data from which the representation is explicitly constructed, up to a possible unramified twist in each block of the parameter. We deduce a Ramification Theorem for $G$, giving a bijection between the set of endo-parameters for $G$ and the set of restrictions to wild inertia of discrete Langlands parameters …
For a classical group over a non-archimedean local field of odd residual characteristic p, we prove that two cuspidal types, defined over an algebraically closed field C of characteristic different from p, intertwine if and only if they are conjugate. This completes work of the first and third authors who showed that every irreducible cuspidal C-representation of a classical group is compactly induced from a cuspidal type. We generalize Bushnell and Henniart's notion of endo-equivalence to semisimple characters of general linear groups and to self-dual semisimple characters of classical groups…
In [Ar13], Arthur classifies the automorphic discrete spectrum of symplectic groups up to global Arthur packets, based on the theory of endoscopy. It is an interesting and basic question to ask: which global Arthur packets contain no cuspidal automorphic representations? The investigation on this question can be regarded as a further development of the topics originated from the classical theory of singular automorphic forms. The results obtained yield a better understanding of global Arthur packets and of the structure of local unramified components of the cuspidal spectrum, and hence are clo…
Let F be a non-archimedean local field of odd residual characteristic p. Let G be a (connected) reductive group that splits over a tamely ramified field extension of F. We show that a construction analogous to Yu's construction of complex supercuspidal representations yields smooth, irreducible, cuspidal representations over an arbitrary algebraically closed field R of characteristic different from p. Moreover, we prove that this construction provides all smooth, irreducible, cuspidal R-representations if p does not divide the order of the Weyl group of G.
Simple cuspidal representations of symplectic groups: Langlands parameter
本文通过显式计算覆盖的 Hecke 代数生成元，确定了非阿基米德局部域上辛群简单尖点表示的 Jordan 集，并在 $p$-进域情形下进一步给出了其朗兰兹参数。
Modular Weil representation and compatibility of cuspidals with congruences
本文研究了在ℓ-模设定下Weil表示的推广，并探讨了自守形式在同余下的相容性问题。
We define a new notion of cuspidality for representations of $\GL_n$ over a finite quotient $\Oh_k$ of the ring of integers $\Oh$ of a non-Archimedean local field $F$ using geometric and infinitesimal induction functors, which involve automorphism groups $G_λ$ of torsion $\Oh$\nobreakdash-modules. When $n$ is a prime, we show that this notion of cuspidality is equivalent to strong cuspidality, which arises in the construction of supercuspidal representations of $\GL_n(F)$. We show that strongly cuspidal representations share many features of cuspidal representations of finite general linear gr…
An analogue of irreducible cuspidal representations for the group $PGL(2)$ over a two-dimensional local field
本文研究了在二维局部域上 $PGL(2)$ 的不可约 cuspidal 表示的类比，通过二次扩张和非 Galois 不变的特征构造了此类表示，并探讨了其在 Borel 子群上的限制性质。
Explicit multiplicities in the cuspidal spectrum of SU(n,1)
本文利用 Selberg 迹公式推导了实李群 SU(n,1) 主同余子群商的可积离散序列表示重数显式公式，并应用于计算局部对称空间的尖点上同调及证明 Dirichlet $L$-函数取值的有理性。
Types and collapse for cuspidal representations of groups acting on trees
本文针对作用于树的群的尖点表示，在之前秩一p进群超尖点表示的几何局部化方法基础上，通过几何极小K型描述诱导数据、证明等变层坍缩为内射层，将相关概念推广至高秩群并提出猜想。
On the potential automorphy and the local-global compatibility for the monodromy operators at $p \neq l$ over CM fields
本文研究了CM域上非l素数处GL_n(A_F)的自守表示的局部-整体兼容性及高维情况下的拉马努金猜想证明。
Number of cuspidal automorphic representations and Hitchin's moduli spaces
本文研究有限域上曲线的函数域中、在指定点集具有固定局部Deligne-Lusztig诱导表示的尖点自守表示计数问题，通过Hitchin模叠的群胚基数给出表达式，并利用Arthur-Selberg迹公式变体证明了几何侧的消失性结果。
Doubling constructions: Global functoriality for non-generic cuspidal representations
针对辛群等群与$GL_k$的表示对，研究广义加倍方法，分析局部积分极点并证明扭曲的整体完备$L$-函数的整性，结合逆定理给出不依赖迹公式的弱函子转移新证明。
Let n be a positive integer, F be a non-Archimedean locally compact field of odd residue characteristic p and G be an inner form of GL(2n,F). This is a group of the form GL(r,D) for a positive integer r and division F-algebra D of reduced degree d such that rd=2n. Let K be a quadratic extension of F in the algebra of matrices of size r with coefficients in D, and H be its centralizer in G. We study selfdual cuspidal representations of G and their distinction by H from the point of view of type theory. Given such a representation pi of G, we compute the value at 1/2 of the epsilon factor of the…
Exceptional poles of local spinor $L$-functions of $\mathrm{GSp}(4)$ with anisotropic Bessel models
本文研究了局部非阿基米德域上 $\mathrm{GSp}(4)$ 非尖点不可约可容许表示，确定了 Piatetski-Shapiro 构造的各向异性贝塞尔模型旋量 $L$-因子的例外极点。
Let $G$ be a split reductive group over a local field $\bK$, and let $G((t))$ be the corresponding loop group. In \cite{GK} we have introduced the notion of a representation of (the group of $\bK$-points) of $G((t))$ on a pro-vector space. In addition, we have defined an induction procedure, which produced $G((t))$-representations from usual smooth representations of $G$. We have conjectured that the induction of a cuspidal irreducible representation of $G$ is irreducible. In this paper we prove this conjecture for $G=SL_2$.
By computing reducibility points of parabolically induced representations, we construct, to within at most two unramified quadratic characters, the Langlands parameter of an arbitrary depth zero irreducible cuspidal representation $π$ of a classical group (which may be not-quasi-split) over a nonarchimedean local field of odd residual characteristic. From this, we can explicitly describe all the irreducible cuspidal representations in the union of one, two, or four L-packets, containing $π$. These results generalize the work of DeBacker-Reeder (in the case of classical groups) from regular to …
We construct all cuspidal l-modular representations of a unitary group in three variables attached to an unramified extension of local fields of odd residual characteristic p with l\neq p. We describe the l-modular principal series and show that the supercuspidal support of an irreducible l-modular representation is unique up to conjugacy.
We construct an endoscopic decomposition for local L-packets associated to irreducible cuspidal Deligne-Lusztig representations. Moreover, the obtained decomposition is compatible with inner twistings.
Generalizations of the Springer correspondence and cuspidal Langlands parameters
本文为约化 p-进群引入增强 Langlands 参数的尖点性概念及 Bernstein 分量，揭示其空间为扭曲扩展商并集，并将 Lusztig 广义 Springer 对应推广到不连通复约化群，从而将局部 Langlands 对应问题归结为 Levi 子群的超尖点表示情形。
Let $k$ be an algebraically closed field of characteristic $l\neq p$. We construct maximal simple cuspidal $k$-types of Levi subgroups $\mathrm{M}'$ of $\mathrm{SL}_n(F)$, when $F$ is a non-archimedean locally compact field of residual characteristic $p$. We show that the supercuspidal support of irreducible smooth $k$-representations of Levi subgroups $\mathrm{M}'$ of $\mathrm{SL}_n(F)$ is unique up to $\mathrm{M}'$-conjugation, when $F$ is either a finite field of characteristic $p$ or a non-archimedean locally compact field of residual characteristic $p$.
On tensor products of regular characters of the general linear and unitary groups of degree two over the principal ideal local rings of finite length
本文研究有限长度主理想局部环上二阶一般线性群和酉群的正则不可约表示的张量积分解，证明不同类型正则表示张量积的重数性质，揭示有限域与一般局部环情形的差异。
Let E/F be a quadratic extension of number fields. For a cuspidal representation $π$ of SL(2,A_E), we study the non-vanishing of the period integral on SL(2,F)\SL(2,A_F). We characterise the non-vanishing of the period integral of $π$ in terms of $π$ being generic with respect to characters of E\A_E which are trivial on A_F. We show that the period integral in general is not a product of local invariant functionals, and find a necessary and sufficient condition when it is. We exhibit cuspidal representations of SL(2,A_E) whose period integral vanishes identically while each local constituent a…
In analogy with the study of representations of $GL_{2n}(F)$ distinguished by $Sp_{2n}(F)$, where $F$ is a local field, in this paper we study representations of $U_{2n}(F)$ distinguished by $Sp_{2n}(F)$. (Only quasi-split unitary groups are considered in this paper since they are the only ones which contain $Sp_{2n}(F)$.) We prove that there are no cuspidal representations of $U_{2n}(F)$ distinguished by $Sp_{2n}(F)$ for $F$ a non-archimedean local field. We also prove the corresponding global theorem that there are no cuspidal representations of $U_{2n}({\mathbb A}_k)$ with nonzero period in…
Discrete series representations of quaternionic ${\rm GL}_n(D)$ with symplectic periods
本文研究了四元数GL_n(D)的离散级数表示，证明了其具有辛周期当且仅当该表示是本原的，并且其Jacquet-Langlands转移至GL_{2n}(F)时是非本原的。
In the first part, we construct a new isomorphism between the endomorphism algebra of an induced cuspidal character sheaf and the group algebra of the relative Weyl group involved. We show it differs from the isomorphism of Lusztig by a linear character, and we relate this linear character to some stabilizers. Some consequences for characteristic functions of character sheaves are obtained. In the second part, we compute explicitly this linear character whenever the cuspidal local system is supported by the regular unipotent class and, as an application of these methods, we obtain a refinement…
A local twisted trace formula for Whittaker induction of coregular symmetric pairs: the geometric side
本文建立余正则对称对 Whittaker 归纳的局部扭曲迹公式几何侧及拟特征标正则芽公式，并推出强尖点测试函数下的局部迹公式、模型重数公式及 L-包相关应用。
Let $F$ be a non-Archimedean local field. An irreducible cuspidal representation of $\text{\rm GL}_n(F)$ is epipelagic if its Swan conductor equals 1. We give a full and explicit description of the Langlands parameters of such representations.
A family of global integrals representing a product of tensor product (partial) $L$-functions: $ L^S(s,π\timesτ_1)L^S(s,π\timesτ_2)... L^S(s,π\timesτ_r) $ are established in this paper, where $π$ is an irreducible cuspidal automorphic representation of a quasi-split classical group of Hermitian type and $τ_1,...,τ_r$ are irreducible unitary cuspidal automorphic representations of $\GL_{a_1},...,\GL_{a_r}$, respectively. When $r=1$ and the classical group is an orthogonal group, this was studied by Ginzburg, Piatetski-Shapiro and Rallis in 1997 and when $π$ is generic and $τ_1,...,τ_r$ are not …
We define etale cohomology of the moduli spaces of mixed characteristic local shtukas so that it gives smooth representations including the case where the relevant elements of the Kottwitz set are both non-basic. Then we relate the etale cohomology of different moduli spaces of mixed characteristic local shtukas using convolution morphisms, duality morphisms and twist morphisms. As an application, we show the Kottwitz conjecture in some new cases including the cases for all inner forms of $\mathrm{GL}_3$ and minuscule cocharacters. We study also some non-minuscule cases and show that the Kottw…
Let $G$ be a simple group over a global function field $K$, and let $π$ be a cuspidal automorphic representation of $G$. Suppose $K$ has two places $u$ and $v$ (satisfying a mild restriction on the residue field cardinality), at which the group $G$ is quasi-split, such that $π_u$ is tempered and $π_v$ is unramified and generic. We prove that $π$ is tempered at all unramified places $K_w$ at which $G$ is unramified quasi-split. The proof uses the Galois parametrization of cuspidal representations due to V. Lafforgue to relate the local Satake parameters of $π$ to Deligne's theory of Frobenius w…
In this paper, we prove the local converse theorem for split even special orthogonal groups over a non-Archimedean local field of characteristic zero. This is the only case left on local converse theorems of split classical groups and the difficulty is the existence of the outer automorphism. We apply new ideas of considering the summation of partial Bessel functions and overcome this difficulty. As a direct application, we obtain a weak rigidity theorem for irreducible generic cuspidal representations of split even special orthogonal groups.
We prove a geometric version of a classical result on the characterization of an irreducible cuspidal automorphic representation of $\mathrm{GL}_n(\mathbb{A}_E)$ being the base change of a stable cuspidal packet of the quasi-split unitary group associated to the quadratic extension $E/F$, via the nonvanishing of certain period integrals, called being distinguished. We show that certain cohomology of an automorphic sheaf of $\mathrm{GL}_{n,X'}$ is nonvanishing if and only if the corresponding local system $E$ on $X'$ is conjugate self-dual with respect to an étale double cover $X'/X$ of curves,…
We present an integral representation for the tensor product $L$-function of a pair of automorphic cuspidal representations, one of a classical group, the other of a general linear group. Our construction is uniform over all classical groups, and is applicable to all cuspidal representations; it does not require genericity. The main new ideas of the construction are the use of generalized Speh representations as inducing data for the Eisenstein series and the introduction of a new (global and local) model, which generalizes the Whittaker model. This is the first in a series of papers, treating…
It is conjectured by Adams-Vogan and Prasad that under the local Langlands correspondence, the L-parameter of the contragredient representation equals that of the original representation composed with the Chevalley involution of the L-group. We verify a variant of their prediction for all connected reductive groups over local fields of positive characteristic, in terms of the local Langlands parameterization of Genestier-Lafforgue. We deduce this from a global result for cuspidal automorphic representations over function fields, which is in turn based on a description of the transposes of V. L…
Gamma factors and root numbers of pairs for the Galois and the linear model
本文利用调和分析将Ok的相对局部逆定理从尖点表示推广到平方可积表示，并证明线性模型变体，同时验证中心值处伽马与epsilon因子的平凡性，并给出Prasad和Ramakrishnan猜想的新证明。
Global liftings between inner forms of GSp(4)
本文研究数域上约化群到其拟分裂内形式的自守提升，证明许多情形下非平凡上同调弱整体提升的存在性，并针对 GSp(4) 内形式解决局部提升的精细细节，证实了 Ibukiyama-Kitayama 关于平方自由水平参数模新形式的猜想。
Generalized Springer Theory for D-modules on a Reductive Lie Algebra
本文建立了约化李代数上等变 D-模范畴的广义 Springer 理论，将其正交分解为以尖点数据为指标的分块，并证明每个分块等价于中心上相对 Weyl 群等变 D-模范畴，核心方法是发展抛物诱导与限制函子及相应单子理论。
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