DOCSLIB.ORG

Supercuspidal Representations of Finite Reductive Groups

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Supercuspidal Representations of Finite Reductive Groups JOURNAL OF ALGEBRA 184, 839]851Ž. 1996 ARTICLE NO. 0287 Supercuspidal Representations of Finite Reductive Groups Gerhard Hiss IWR der Uni¨ersitatÈ Heidelberg, Im Neuenheimer Feld 368, D-69120 Heidelberg, Germany View metadata, citation and similar papersCommunicated at core.ac.uk by Michel Broue brought to you by CORE provided by Elsevier - Publisher Connector Received January 9, 1995 DEDICATED TO MY PARENTS 1. INTRODUCTION A powerful tool in representation theory of finite groups of Lie type is Harish]Chandra induction. It is a method to construct, in a systematic way, representations for the group from those ofŽ. split Levi subgroups. Let G be a finite group of Lie type. An irreducible representationŽ of finite degree over a field containing the <<G th roots of unity. of G is called cuspidal if it does not occur as a subrepresentation of a Harish]Chandra induced representation of a proper Levi subgroup. In order to find all irreducible representations of G, one has to construct the cuspidal repre- sentations of all Levi subgroups first. Then one has to find all irreducible subrepresentations of Harish]Chandra induced cuspidal representations. Some of the cuspidal representations may occur as subquotients of Harish]Chandra induced representations. Following Vigneras, we call an irreducible representation of G super- cuspidal if it does not occur as a subquotient of a Harish]Chandra induced representation of a proper Levi subgroup. Thus, in particular, a supercuspidal representation is cuspidal. If the characteristic of the under- lying field does not divide the order of G, all representations of G are semisimple, so each subquotient is also a subrepresentation. In this case, a cuspidal representation is supercuspidal. In this paper, motivated by a suggestion of Vigneras, we begin a systematic investigation of the supercuspidal irreducible representations of finite groups of Lie type. We conjecture that a supercuspidal representa- 839 0021-8693r96 $18.00 Copyright Q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved. 840 GERHARD HISS tion is liftable to characteristic 0. This is related to a conjecture of Geck. We show that an irreducible representation is supercuspidal if and only if every composition factor of its projective cover is cuspidal. We then determine all supercuspidal unipotent representations of the classical groupsŽ. in odd characteristics and also of some exceptional groups of Lie type. The results indicate that a complete classification of all supercuspidal representations seems to be possible. 2. SUPERCUSPIDAL MODULES Let G be a finite group with a split BN-pair of characteristic p. Let L denote the set of all conjugates of standard Levi subgroups of G. Let k be a field which is a splitting field for every subgroup of G.We assume that the characteristic l of k is different from p. All modules G considered will be finitely generated. For L g L we denote by RL the functor Harish]Chandra induction, mapping finitely generated kL-modules to finitely generated kG-modules. The adjoint functor Harish]Chandra U G restriction or truncation is denoted by RL . We refer the reader tow 7, Sect. 1x for a general discussion of these functors. Harish]Chandra induction and restriction preserve projective modules. XX DEFINITION 2.1Ž Vigneraswx 29.Ž . For L, M .Ž, L, M .in the set W [ Ä4Ž.L, MLgL,Ma simple kL-moduleŽ up to isomorphism. , XX XX define ŽL, M .ŽF L, M .if and only if L F L and M is isomorphic to a U L XX XŽ. Ž .Ž . composition factor of RML . Define L, M 1 L, M if and only if X L X X Ž . L F L and M is isomorphic to a composition factor of RML . It is then easy to check that the relations F and 1 are partial orderings on W .If Ž.L,Mis a minimal element of W with respect to 1 , then M is called a supercuspidal simple kL-module. Remark 2.2. A kG-module M is called cuspidalŽ cf.wx 7, Definition 2.5 . if U L RLX Ž.M s 0 X X for all L g L with L strictly contained in L. It is easy to see that a kG-module is cuspidal if and only if each of its composition factors is. If M is a simple kL-module for some L g L , then M is cuspidal if and only if Ž.L,Mis a minimal element of W with respect to F . PROPOSITION 2.3. Let M be a simple kG-module. Then M is supercuspidal if and only if its projecti¨eco¨er PM is cuspidal. SUPERCUSPIDAL REPRESENTATIONS 841 Proof. We have G U G Hom kGŽ.Ž.P M, RV L Ž.(Hom kLRP LŽ. M ,V Ž.1 for every Levi subgroup L and every kL-module V. Now M is supercuspi- dal if and only if the left-hand side ofŽ. 1 is zero for every L g L properly contained in G and every kL-module V. On the other hand, PM is cuspidal if and only if the right-hand side ofŽ. 1 is zero for every such pair Ž.L, V . Remarks 2.4.Ž. a It follows from Proposition 2.3 that a supercuspidal module is cuspidal. Examples below show that the converse is not true in general. Ž.b Proposition 2.3 can be used to extend the definition of supercuspi- dal modules to arbitrary finitely generated kG-modules M. We say that M is supercuspidal if and only if PM is cuspidal. This is the case if and only if every composition factor of MrradŽ.M is supercuspidal. Ž.c Let G12and G denote groups with split BN-pairs of characteristic Ž p. Let Miidenote simple kM -modules, i s 1, 2. Then the simple kG1= . G212-module M m M is supercuspidal, if and only if each Miis. Ž.d Let MU denote the module contragradientŽ. dual to the kG-mod- ule M.If Mis simple, then M is supercuspidal if and only if MU is. 1 Ž.e Let M, V be simple kG-modules with Ext kGŽ.M, V / 0. If one of M or V is supercuspidal, then the other one is cuspidal. Ž.f If a cuspidal simple kG-module is in a block of defect zero, then it is supercuspidal. QUESTION 2.5. Let V be a simple kG-module. Then there is a minimal elementŽ.Ž.Ž. L, M 1 G, V . Is L, M uniquely determined Ž up to conjuga- tion. by V ? The corresponding question for cuspidal simple modules has an affirma- tive answerŽ seewx 22, Theorem 5.5. 3. A CONJECTURE FOR FINITE REDUCTIVE GROUPS Let G be a connected reductive algebraic group which is defined over the finite field Fq with q elements. Let F denote the Frobenius endomor- F phism corresponding to this Fq-structure on G. The set G s G of fixed points of F on G is called a finite reductive group or a finite group of Lie type. It is a group with a split BN-pair of characteristic p dividing q. We choose a prime l different from p and a splitting l-modular system Ž.ŽK,R,kfor G where K is a finite extension of Ql .. Let s be an F-stable semisimple element in the dual group GU. Its GU F-conjugacy class is 842 GERHARD HISS denoted by wxs , and the corresponding rational Lusztig series of irreducible K-characters of G by EŽG, wxs .Žseewx 5, p. 136 for the definition. Now suppose that s is also l-regular, i.e., its order is not divisible by l. Then, by a result of Broue and Michelwx 2 , ElŽ.G,wxs [ E ŽG,wts x . DF tgCsGUŽ.t F is a union of l-blocks. Here, CsGUŽ.l is the set of F-stable l-elements in GU centralizing s. Conjecture 3.1. Let G be a finite reductive group and M a supercuspi- dal simple kG-module contained in ElŽG, wxs .. Then M is liftable to an RG-lattice whose character is contained in EŽG, wxs .. It is interesting to compare Conjecture 3.1 with a conjecture of Geck. Conjecture 3.2Ž Geckw 15,Ž. 6.6x. The cuspidal simple KG-modules in the rational Lusztig series EŽG, wxs .remain simple on reduction modulo l. PROPOSITION 3.3. The truth of Geck's Conjecture 3.2 implies the truth of Conjecture 3.1. Proof. Let M denote a supercuspidal simple kG-module. Then, by Proposition 2.3, the projective module PM is cuspidal. In particular, all ordinary constituents ofŽ. the lift of PM are cuspidal. Now M and hence also PMllie in a union of blocks E ŽG, wxs .. Byw 20, Theorem 3.1x there is a simple KG-module X contained in EŽG, wxs .such that M is a composition factor in a reduction modulo l of X. By Brauer reciprocity, X is a constituent of the lift of PM . Hence X is cuspidal. If Geck's conjecture is true, the reduction modulo l of X is simple, hence isomorphic to M. In other words, M is liftable. Geck's conjecture is known to be true for the groups GL nŽ.q w6, Theorem 3.5x and GUnŽ.q wx17, Theorem 6.10 , as well as for split classical groups and l s 2 Ž.q largewx 18, Theorem 4.4 . It is also true for some 3 exceptional groups such as Gq24Ž.wx19, 25, 24 and DqŽ.wx14 . Furthermore, it is known to be true in some cases for the unipotent cuspidal characters of Eq64Ž.wx16 and for FqŽ.wx30 .
Load more

Recommended publications
  • CUSPIDAL IRREDUCIBLE COMPLEX OR L-MODULAR REPRESENTATIONS of QUATERNIONIC FORMS of P-ADIC CLASSICAL GROUPS for ODD P
    CUSPIDAL IRREDUCIBLE COMPLEX OR l-MODULAR REPRESENTATIONS OF QUATERNIONIC FORMS OF p-ADIC CLASSICAL GROUPS FOR ODD p DANIEL SKODLERACK Abstract. Given a quaternionic form G of a p-adic classical group (p odd) we clas- sify all cuspidal irreducible representations of G with coefficients in an algebraically closed field of characteristic different from p. We prove two theorems: At first: Every irreducible cuspidal representation of G is induced from a cuspidal type, i.e. from a certain irreducible representation of a compact open subgroup of G, constructed from a β-extension and a cuspidal representation of a finite group. Secondly we show that two intertwining cuspidal types of G are up to equivalence conjugate under some ele- ment of G. [11E57][11E95][20G05][22E50] 1. Introduction This work is the third part in a series of three papers, the first two being [35] and [37]. Let F be a non-Archimedean local field with odd residue characteristic p. The construc- tion and classification of cuspidal irreducible representation complex or l-modular of the set of rational points G(F) of a reductive group G defined over F has already been success- fully studied for general linear groups (complex case: [11] Bushnell{Kutzko, [31], [4], [32] Broussous{Secherre{Stevens; modular case: [44] Vigneras, [23] Minguez{Sech´erre)and for p-adic classical groups ([42] Stevens, [21] Kurinczuk{Stevens, [20] Kurinczuk{Stevens joint with the author). In this paper we are generalizing from p-adic classical groups to their quaternionic forms. Let us mention [46] Yu, [15], [16] Fintzen and [19] Kim for results over reductive p-adic groups in general.
    [Show full text]
  • Arxiv:2102.03100V1 [Math.NT]
    L The special values of the standard -functions for GSp2n × GL1 Shuji Horinaga, Ameya Pitale, Abhishek Saha, Ralf Schmidt Abstract We prove the expected algebraicity property for the critical L-values of character twists of the standard L-function associated to vector-valued holomorphic Siegel cusp forms of archimedean type (k1, k2,...,kn), where kn ≥ 2n + 2 and all ki are of the same parity. For the proof, we use an explicit integral representation to reduce to arithmetic properties of differential operators on vector-valued nearly holomorphic Siegel cusp forms. We establish these properties via a representation-theoretic approach. Contents 1 Introduction 1 1.1 Notation........................................ 4 2 Lie algebra action and differential operators 5 2.1 Basics on the Lie algebra of Sp2n(R)......................... 6 2.2 Generators for the center of the universal enveloping algebra ........... 7 2.3 Differentialoperators. ..... 8 2.4 The relationship between elements of U(gC) and differential operators . 9 2.5 Scalar and vector-valued automorphic forms . ........... 10 3 Nearly holomorphic Siegel modular forms 14 3.1 Definitionsandbasicproperties . ........ 14 3.2 Nearly holomorphic modular forms and (p−)-finite automorphic forms . 15 3.3 Action of Aut(C).................................... 18 3.4 Arithmeticity of certain differential operators on nearly holomorphic cusp forms . 24 4 Special values of L-functions 28 arXiv:2102.03100v1 [math.NT] 5 Feb 2021 4.1 Automorphicrepresentations . ....... 28 4.2 Classicalandadeliccuspforms . ....... 29 4.3 Eisensteinseries ................................ .... 32 4.4 Algebraicity of critical L-values............................ 32 Bibliography 34 1 Introduction The arithmetic of special values of L-functions is of great interest in modern number theory.
    [Show full text]
  • Whittaker–Fourier Coefficients of Cusp Forms
    WHITTAKER{FOURIER COEFFICIENTS OF CUSP FORMS ZHENGYU MAO Abstract. We report on the work with E. Lapid about a conjecture relating Whittaker- Fourier coefficients of cusp forms to special values of L−functions. Contents 1. Introduction 1 2. Statement of the conjecture 2 3. Some known cases 5 4. Case of classical group and metaplectic group: automorphic descent 6 References 10 1. Introduction Let G be a quasi-split reductive group over a number field F and A the ring of adeles of F . Let B be a Borel subgroup of G defined over F , N the unipotent radical of B and fix a non-degenerate character N of N(A), trivial on N(F ). For a cusp form ' of G(F )nG(A) we consider the Whittaker{Fourier coefficient Z N −1 −1 W(') = W (') := (vol(N(F )nN(A))) '(n) N (n) dn: N(F )nN(A) If π is an irreducible cuspidal representation then W, if non-zero, gives a realization of π in the space of Whittaker functions on G(A), which by local multiplicity one depends only on π as an abstract representation. It therefore provides a useful tool for understanding π, both computationally and conceptually. It is natural to study the size of W('). In [LM15], inspired by the work of Ichino-Ikeda [II10], with E. Lapid we made a conjecture relating the size of W(') with a special L−value of π. In this note, we report on the work with Lapid on this conjecture. In modular form language, the notion of Whittaker-Fourier coefficient is roughly that of Fourier coefficient of a modular form.
    [Show full text]
  • Max-Planck-Institut Für Mathematik Bonn
    Max-Planck-Institut für Mathematik Bonn Non-vanishing square-integrable automorphic cohomology classes - the case GL(2) over a central division algebra by Joachim Schwermer Max-Planck-Institut für Mathematik Preprint Series 2020 (48) Date of submission: September 10, 2020 Non-vanishing square-integrable automorphic cohomology classes - the case GL(2) over a central division algebra by Joachim Schwermer Max-Planck-Institut für Mathematik Faculty of Mathematics Vivatsgasse 7 University Vienna 53111 Bonn Oskar-Morgenstern-Platz 1 Germany 1090 Vienna Austria MPIM 20-48 1 NON-VANISHING SQUARE-INTEGRABLE AUTOMORPHIC 2 COHOMOLOGY CLASSES - THE CASE GL(2) OVER A CENTRAL 3 DIVISION ALGEBRA 4 JOACHIM SCHWERMER Abstract. Let k be a totally real algebraic number field, and let D be a central divi- sion algebra of degree d over k. The connected reductive algebraic k-group GL(2;D)=k has k-rank one; it is an inner form of the split k-group GL(2d)=k. We construct auto- morphic representations π of GL(2d)=k which occur non-trivially in the discrete spec- trum of GL(2d; k) and which have specific local components at archimedean as well as non-archimedean places of k so that there exist automorphic representations π0 of 0 GL(2;D)(Ak) with Ξ(π ) = π under the Jacquet-Langlands correspondence. These re- quirements depend on the finite set VD of places of k at which D does not split, and on 0 the quest to construct representations π of GL(2;D)(Ak) which either represent cusp- idal cohomology classes or give rise to square-integrable classes which are not cuspidal, that is, are eventually represented by a residue of an Eisenstein series.
    [Show full text]
  • Arxiv:1404.0861V1 [Math.RT] 3 Apr 2014 St Td the Study to Is Rbe Foei Neetdi Opeecaatrinformat Character Complete in Interested Understood
    NOTES ON REPRESENTATIONS OF FINITE GROUPS OF LIE TYPE DIPENDRA PRASAD These are the notes of some lectures given by the author for a workshop held at TIFR in December, 2011, giving an exposition of the Deligne-Lusztig theory. The aim of these lectures was to give an overview of the subject with several examples without burdening them with detailed proofs of the theorems involved for which we refer to the original paper of Deligne and Lusztig, as well as the beautiful book of Digne and Michel on the subject. The author thanks Shripad M. Garge for writing and texing the first draft of these notes. Contents 1. Preliminaries on Algebraic groups 2 2. Classical groups and tori 3 3. Some Exceptional groups 5 4. Basic notions in representation theory 6 5. The Deligne-Lusztig theory 7 6. Unipotent cuspidal representations 9 7. The Steinberg representation 9 8. Dimension of the Deligne-Lusztig representation 10 9. The Jordan decomposition of representations 11 10. Exercises 12 11. References 13 arXiv:1404.0861v1 [math.RT] 3 Apr 2014 The Deligne-Lusztig theory constructs certain (virtual) representations of G(Fq) denoted as RG(T, θ) where G is a connected reductive algebraic group defined over Fq, T is a maximal torus in G defined ∼ × over F and θ is a character of T (F ), θ : T (F ) C× Q . The representation R (T, θ) is called q q q → −→ l G the Deligne-Lusztig induction of the character θ of T (Fq) to G(Fq), generalizing parabolic induction with which it coincides when T is a maximally split maximal torus in G.
    [Show full text]
  • SUPERCUSPIDAL REPRESENTATIONS of Glnpfq DISTINGUISHED by a GALOIS INVOLUTION
    SUPERCUSPIDAL REPRESENTATIONS OF GLnpFq DISTINGUISHED BY A GALOIS INVOLUTION by Vincent Sécherre Abstract.— Let F{F0 be a quadratic extension of non-Archimedean locally compact fields of resi- dual characteristic p ‰ 2, and let σ denote its non-trivial automorphism. Let R be an algebraically closed field of characteristic different from p. To any cuspidal representation π of GLnpFq, with coef- ficients in R, such that πσ » π_ (such a representation is said to be σ-selfdual) we associate a quadra- tic extension D{D0, where D is a tamely ramified extension of F and D0 is a tamely ramified exten- ˆ sion of F0, together with a quadratic character of D0 . When π is supercuspidal, we give a necessary and sufficient condition, in terms of these data, for π to be GLnpF0q-distinguished. When the charac- ˆ teristic ` of R is not 2, denoting by ω the non-trivial R-character of F0 trivial on F{F0-norms, we prove that any σ-selfdual supercuspidal R-representation is either distinguished or ω-distinguished, but not both. In the modular case, that is when ` ¡ 0, we give examples of σ-selfdual cuspidal non- supercuspidal representations which are not distinguished nor ω-distinguished. In the particular case where R is the field of complex numbers, in which case all cuspidal representations are supercuspi- dal, this gives a complete distinction criterion for arbitrary complex cuspidal representations, as well as a purely local proof, for cuspidal representations, of the dichotomy and disjunction theorem due to Kable and Anandavardhanan–Kable–Tandon, when p ‰ 2.
    [Show full text]
  • On the Computation of Local Components of a Newform 3
    ON THE COMPUTATION OF LOCAL COMPONENTS OF A NEWFORM DAVID LOEFFLER AND JARED WEINSTEIN 1. Introduction 1.1. The problem. Let f be a cuspidal newform for Γ1(N) with weight k 2 and character ε. There are well-established methods for computing such forms≥ using modular symbols, see [Ste07]. Let πf be the corresponding automorphic representa- tion of the ad`ele group GL2(AQ). (As there are numerous possible normalisations, we shall recall the construction in section 2.1 below.) This representation decom- poses as a restricted tensor product over all places v of Q: πf = πf,v, v O where πf,v is an irreducible admissible representation of GL2(Qv). The isomor- phism class of the infinite component πf,∞ is determined by the weight k alone: it is the unique discrete series subrepresentation of the representation constructed via unitary induction from the character k/2 t1 t1 k ∗ sgn(t1) t2 7→ t 2 of the Borel subgroup of GL2(R) [Gel75, prop. 5.21]. Similarly, the component πf,p for a prime p ∤ N is the unramified principal series with Satake parameters equal 2 k−1 to the roots of the polynomial X apX + ε(p)p . We are led naturally to the following problem: − Problem 1.1. Compute the local components π for each prime p N. f,p | Problem 1.1 may be recast from an arithmetic perspective as a question about the local behavior of Galois representations. Suppose the Fourier coefficients of f arXiv:1008.2796v1 [math.NT] 17 Aug 2010 lie in a number field E.
    [Show full text]
  • GEOMETRY of DUAL SPACES of REDUCTIVE GROUPS (Non-Archimedean Case)
    GEOMETRY OF DUAL SPACES OF REDUCTIVE GROUPS (non-archimedean case) MARKO TADIC Department of Mathematics, University of Zagreb, P.O. Box 187, 41001 Zagreb, Yugoslavia Introduction J. M. G. Fell introduced in [ 1O] the notion of the non-unitary dual space of a locally compact group. By his definition, it is a topological space. The main part of that paper deals with the basic properties of the topology of non-unitary dual space. This paper can be considered mainly as a continuation of such investi- gations, in the case of a p-adic reductive group G. We write down proofs of the basic properties of this topological space for such G. Since in the last twenty years after the appearance of [ 10] the topology of non-unitary dual has not attracted much attention, we begin with a longer introduction explaining motivations and reasons for writing this paper. Let G be a connected reductive group over a non-archimedean local field F. The set of all equivalence classes of topologically irreducible unitary represen- tations of G is denoted by G. The set d is in a natural way a topological space. The topology may be described in terms of approximation of matrix coefficients. In the study of some topological space a first reduction may be to decompose it into disjoint union of open and closed subsets. In [26] such a decomposition of G was obtained. One could see easily that the decomposition in [26] was not the finest possible of such type. This author realized that the right setting for the decompo- sition in [26] of (~ is not G but another topological space.
    [Show full text]
  • Remark on Representation Theory of General Linear Groups Over a Non-Archimedean Local Division Algebra
    REMARK ON REPRESENTATION THEORY OF GENERAL LINEAR GROUPS OVER A NON-ARCHIMEDEAN LOCAL DIVISION ALGEBRA MARKO TADIC´ Abstract. 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 lo- cal 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 reduc- tive p-adic groups (the theory that we use was completed more then three decades ago, mainly in 1970-es). Of the specific results for general linear groups over A, basically we use only a very old result of G.I. Ol'ˇsanskiˇi, which says that there exist complementary series starting from Ind(ρ⊗ρ) whenever ρ is a unitary irreducible cuspidal representation. In appendix of [11], there is also a simple local proof of these results, based on a slightly different approach. 1. Introduction Let A be a local non-archimedean division algebra. Two major steps in classifying unitary duals of general linear groups over a local non-archimedean division algebra A modulo cuspidal representations, were done in [3] by D. Renard and I. Badulescu, and in [16] by V. S´echerre. The unitarizability of Speh representations was proved in [3] using global methods (and a simple form of the trace formula of Arthur1).
    [Show full text]
  • Motives and Automorphic Representations Laurent Clozel
    Motives and automorphic representations Laurent Clozel To cite this version: Laurent Clozel. Motives and automorphic representations. 2006. hal-01019707 HAL Id: hal-01019707 https://hal.archives-ouvertes.fr/hal-01019707 Preprint submitted on 7 Jul 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Motives and automorphic representations L. Clozel Introduction These are, slightly expanded, the notes of my 3-hour lecture at IHES in July 2006. The organizers had assigned me two tasks. First, to give an overview of the conjectural relations between the motives defined by algebraic varieties over number fields and automorphic forms { here, automorphic forms on GL(n). (The relation is mediated by two other kinds of objects, namely, Galois representations and L-functions). Secondly, to furnish { in a more leisurely way, at least for the topics I chose to present, than in his paper { the prerequisites necessary to understand the automorphic part of R. Taylor's beautiful lecture, \Galois representations", at the Beijing ICM (2002)1. These are rather succinct notes, so it was certainly not possible to present in detail, with proofs, the basic material: the reader will have to consult the standard references [36, 44, 18].
    [Show full text]
  • NOTES on the ARITHMETIC of HILBERT MODULAR FORMS 1. Introduction Shimura Proved the Following Fundamental Result (See [37, Theor
    NOTES ON THE ARITHMETIC OF HILBERT MODULAR FORMS A. RAGHURAM AND NAOMI TANABE 1. Introduction Shimura proved the following fundamental result (see [37, Theorem 4.3]) on the critical values of the standard L-function attached to a holomorphic Hilbert modular form. Theorem 1.1 (Shimura). Let f be a primitive holomorphic Hilbert modular cusp form of type (k; !~) over a totally real number field F of degree n. Assume that the weight k = (k1; : : : ; kn) satisfies the parity condition k1 ≡ · · · ≡ kn (mod 2): 0 σ Let k = min(k1; : : : ; kn) and k0 = max(k1; : : : ; kn). There exist nonzero complex numbers u(r; f ) defined n n × for r 2 Z =2Z and σ 2 Aut(C) such that for any Hecke character χ of AF of finite order, for any integer m with 0 0 (k0 − k )=2 < m < (k0 + k )=2; and for any σ 2 Aut(C), we have L (m; f; χ) L (m; f σ; χσ) σ f = f ; (2πi)mn τ(χ) u(, f) (2πi)mn τ(χσ) u(, f σ) where is prescribed by: χ(a) = sgn[aN(a)m]; the quantity τ(χ) is the Gauss sum attached to χ, and Lf (s; f; χ) is the (finite part of the) standard L-function attached to f, twisted by χ. The purpose of this semi-expository article is to give another proof of the above theorem, which is rather different from Shimura's proof. However, before proceeding any further, let us mention that our proof is contained in the union of these papers: Harder [18], Hida [21]; see also Dou [10].
    [Show full text]
  • Representation Theory of Groups
    MAT 445/1196 - INTRODUCTION TO REPRESENTATION THEORY CHAPTER 1 – Representation Theory of Groups - Algebraic Foundations 1.1 Basic definitions, Schur’s Lemma 1.2 Tensor products 1.3 Unitary representations 1.4 Characters of finite-dimensional representations CHAPTER 2 – Representations of Finite Groups 2.1 Unitarity, complete reducibility, orthogonality relations 2.2 Character values as algebraic integers, degree of an irreducible representation divides the order of the group 2.3 Decomposition of finite-dimensional representations 2.4 Induced Representations, Frobenius reciprocity, and Frobenius character formula CHAPTER 3 – Representations of SL2(Fq) CHAPTER 4 – Representations of Finite Groups of Lie Type CHAPTER 5 – Topological Groups, Representations, and Haar Measure 5.1 Topological spaces 5.2 Topological groups 5.3 General linear groups and matrix groups 5.4 Matrix Lie groups 5.5 Finite-dimensional representations of topological groups and matrix Lie groups 5.6 Groups of t.d. type 5.7 Haar measure on locally compact groups 5.8 Discrete series representations 5.9 Parabolic subgroups and representations of reductive groups CHAPTER 6 – Representations of Compact Groups 6.1 Examples of compact groups 6.2 Finite-dimensional representations of compact groups 6.3 The Peter-Weyl Theorem 6.4 Weyl’s character formula 1 CHAPTER 1 Representation Theory of Groups - Algebraic Foundations 1.1. Basic definitions, Schur’s Lemma We assume that the reader is familiar with the fundamental concepts of abstract group theory and linear algebra. A representation of a group G is a homomorphism from G to the group GL(V ) of invertible linear operators on V , where V is a nonzero complex vector space.
    [Show full text]