A NEW APPROACH to UNRAMIFIED DESCENT in BRUHAT-TITS THEORY by Gopal Prasad
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Debashish Goswami Jyotishman Bhowmick Quantum Isometry Groups Infosys Science Foundation Series
Infosys Science Foundation Series in Mathematical Sciences Debashish Goswami Jyotishman Bhowmick Quantum Isometry Groups Infosys Science Foundation Series Infosys Science Foundation Series in Mathematical Sciences Series editors Gopal Prasad, University of Michigan, USA Irene Fonseca, Mellon College of Science, USA Editorial Board Chandrasekhar Khare, University of California, USA Mahan Mj, Tata Institute of Fundamental Research, Mumbai, India Manindra Agrawal, Indian Institute of Technology Kanpur, India S.R.S. Varadhan, Courant Institute of Mathematical Sciences, USA Weinan E, Princeton University, USA The Infosys Science Foundation Series in Mathematical Sciences is a sub-series of The Infosys Science Foundation Series. This sub-series focuses on high quality content in the domain of mathematical sciences and various disciplines of mathematics, statistics, bio-mathematics, financial mathematics, applied mathematics, operations research, applies statistics and computer science. All content published in the sub-series are written, edited, or vetted by the laureates or jury members of the Infosys Prize. With the Series, Springer and the Infosys Science Foundation hope to provide readers with monographs, handbooks, professional books and textbooks of the highest academic quality on current topics in relevant disciplines. Literature in this sub-series will appeal to a wide audience of researchers, students, educators, and professionals across mathematics, applied mathematics, statistics and computer science disciplines. More information -
Chapter 25 Finite Simple Groups
Chapter 25 Finite Simple Groups Chapter 25 Finite Simple Groups Historical Background Definition A group is simple if it has no nontrivial proper normal subgroup. The definition was proposed by Galois; he showed that An is simple for n ≥ 5 in 1831. It is an important step in showing that one cannot express the solutions of a quintic equation in radicals. If possible, one would factor a group G as G0 = G, find a normal subgroup G1 of maximum order to form G0/G1. Then find a maximal normal subgroup G2 of G1 and get G1/G2, and so on until we get the composition factors: G0/G1,G1/G2,...,Gn−1/Gn, with Gn = {e}. Jordan and Hölder proved that these factors are independent of the choices of the normal subgroups in the process. Jordan in 1870 found four infinite series including: Zp for a prime p, SL(n, Zp)/Z(SL(n, Zp)) except when (n, p) = (2, 2) or (2, 3). Between 1982-1905, Dickson found more infinite series; Miller and Cole showed that 5 (sporadic) groups constructed by Mathieu in 1861 are simple. Chapter 25 Finite Simple Groups In 1950s, more infinite families were found, and the classification project began. Brauer observed that the centralizer has an order 2 element is important; Feit-Thompson in 1960 confirmed the 1900 conjecture that non-Abelian simple group must have even order. From 1966-75, 19 new sporadic groups were found. Thompson developed many techniques in the N-group paper. Gorenstein presented an outline for the classification project in a lecture series at University of Chicago in 1972. -
Prescribed Gauss Decompositions for Kac-Moody Groups Over Fields
RENDICONTI del SEMINARIO MATEMATICO della UNIVERSITÀ DI PADOVA JUN MORITA EUGENE PLOTKIN Prescribed Gauss decompositions for Kac- Moody groups over fields Rendiconti del Seminario Matematico della Università di Padova, tome 106 (2001), p. 153-163 <http://www.numdam.org/item?id=RSMUP_2001__106__153_0> © Rendiconti del Seminario Matematico della Università di Padova, 2001, tous droits réservés. L’accès aux archives de la revue « Rendiconti del Seminario Matematico della Università di Padova » (http://rendiconti.math.unipd.it/) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit conte- nir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ Prescribed Gauss Decompositions for Kac-Moody Groups Over Fields. JUN MORITA(*) - EUGENE PLOTKIN (**) ABSTRACT - We obtain the Gauss decomposition with prescribed torus elements for a Kac-Moody group over a field containing sufficiently many elements. 1. Introduction. Kac-Moody groups are equipped with canonical decompositions of different types. Let us note, for instance, the decompositions of Bruhat, Birkhoff and Gauss. As in the finite dimensional case, they play an im- portant role in calculations with these groups. However, in the Kac-Moo- dy case each of these decompositions has its own special features (see, for example, [18] where J. Tits compares the Bruhat and the Birkhoff decompositions and presents some applications). The aim of this paper is to establish the so-called prescribed Gauss decomposition for Kac-Moody groups. -
CURTIS-TITS GROUPS GENERALIZING KAC-MOODY GROUPS of TYPE Aen−1
CURTIS-TITS GROUPS GENERALIZING KAC-MOODY GROUPS OF TYPE Aen−1 RIEUWERT J. BLOK AND CORNELIU G. HOFFMAN Abstract. In [13] we define a Curtis-Tits group as a certain generalization of a Kac- Moody group. We distinguish between orientable and non-orientable Curtis-Tits groups and identify all orientable Curtis-Tits groups as Kac-Moody groups associated to twin- buildings. In the present paper we construct all orientable as well as non-orientable Curtis-Tits groups with diagram Aen−1 (n ≥ 4) over a field k of size at least 4. The resulting groups are quite interesting in their own right. The orientable ones are related to Drinfeld’s construction of vector bundles over a non-commutative projective line and to the classical groups over cyclic algebras. The non-orientable ones are related to expander graphs [14] and have symplectic, orthogonal and unitary groups as quotients. Keywords: Curtis-Tits groups, Kac-Moody groups, Moufang, twin-building, amalgam, opposite. MSC 2010: 20G35 51E24 1. Introduction The theory of the infinite dimensional Lie algebras called Kac-Moody algebras was ini- tially developed by Victor Kac and Robert Moody. The development of a theory of Kac- Moody groups as analogues of Chevalley groups was made possible by the work of Kac and Peterson. In [44] J. Tits gives an alternative definition of a group of Kac-Moody type as being a group with a twin-root datum, which implies that they are symmetry groups of Moufang twin-buildings. In [2] P. Abramenko and B. Mühlherr generalize a celebrated theorem of Curtis and Tits on groups with finite BN-pair [18, 42] to groups of Kac-Moody type. -
Tata Institute of Fundamental Research Prof
Annual Report 1988-89 Tata Institute of Fundamental Research Prof. M. G. K. Menon inaugurating the Pelletron Accelerator Facility at TIFR on December 30, 1988. Dr. S. S. Kapoor, Project Director, Pelletron Accelerator Facility, explaining salient features of \ Ion source to Prof. M. G. K. Menon, Dr. M. R. Srinivasan, and others. Annual Report 1988-89 Contents Council of Management 3 School of Physics 19 Homi Bhabha Centre for Science Education 80 Theoretical Physics l'j Honorary Fellows 3 Theoretical A strophysics 24 Astronomy 2') Basic Dental Research Unit 83 Gravitation 37 A wards and Distinctions 4 Cosmic Ray and Space Physics 38 Experimental High Energy Physics 41 Publications, Colloquia, Lectures, Seminars etc. 85 Introduction 5 Nuclear and Atomic Physics 43 Condensed Matter Physics 52 Chemical Physics 58 Obituaries 118 Faculty 9 Hydrology M Physics of Semi-Conductors and Solid State Electronics 64 Group Committees 10 Molecular Biology o5 Computer Science 71 Administration. Engineering Energy Research 7b and Auxiliary Services 12 Facilities 77 School of Mathematics 13 Library 79 Tata Institute of Fundamental Research Homi Bhabha Road. Colaba. Bombav 400005. India. Edited by J.D. hloor Published by Registrar. Tata Institute of Fundamental Research Homi Bhabha Road, Colaba. Bombay 400 005 Printed bv S.C. Nad'kar at TATA PRESS Limited. Bombay 400 025 Photo Credits Front Cover: Bharat Upadhyay Inside: Bharat Upadhyay & R.A. A chary a Design and Layout by M.M. Vajifdar and J.D. hloor Council of Management Honorary Fellows Shri J.R.D. Tata (Chairman) Prof. H. Alfven Chairman. Tata Sons Limited Prof. S. Chandrasekhar Prof. -
FINITE GROUP ACTIONS on REDUCTIVE GROUPS and BUILDINGS and TAMELY-RAMIFIED DESCENT in BRUHAT-TITS THEORY by Gopal Prasad Dedicat
FINITE GROUP ACTIONS ON REDUCTIVE GROUPS AND BUILDINGS AND TAMELY-RAMIFIED DESCENT IN BRUHAT-TITS THEORY By Gopal Prasad Dedicated to Guy Rousseau Abstract. Let K be a discretely valued field with Henselian valuation ring and separably closed (but not necessarily perfect) residue field of characteristic p, H a connected reductive K-group, and Θ a finite group of automorphisms of H. We assume that p does not divide the order of Θ and Bruhat-Tits theory is available for H over K with B(H=K) the Bruhat-Tits building of H(K). We will show that then Bruhat-Tits theory is also available for G := (HΘ)◦ and B(H=K)Θ is the Bruhat-Tits building of G(K). (In case the residue field of K is perfect, this result was proved in [PY1] by a different method.) As a consequence of this result, we obtain that if Bruhat-Tits theory is available for a connected reductive K-group G over a finite tamely-ramified extension L of K, then it is also available for G over K and B(G=K) = B(G=L)Gal(L=K). Using this, we prove that if G is quasi-split over L, then it is already quasi-split over K. Introduction. This paper is a sequel to our recent paper [P2]. We will assume fa- miliarity with that paper; we will freely use results, notions and notations introduced in it. Let O be a discretely valued Henselian local ring with valuation !. Let m be the maximal ideal of O and K the field of fractions of O. -
Title: Algebraic Group Representations, and Related Topics a Lecture by Len Scott, Mcconnell/Bernard Professor of Mathemtics, the University of Virginia
Title: Algebraic group representations, and related topics a lecture by Len Scott, McConnell/Bernard Professor of Mathemtics, The University of Virginia. Abstract: This lecture will survey the theory of algebraic group representations in positive characteristic, with some attention to its historical development, and its relationship to the theory of finite group representations. Other topics of a Lie-theoretic nature will also be discussed in this context, including at least brief mention of characteristic 0 infinite dimensional Lie algebra representations in both the classical and affine cases, quantum groups, perverse sheaves, and rings of differential operators. Much of the focus will be on irreducible representations, but some attention will be given to other classes of indecomposable representations, and there will be some discussion of homological issues, as time permits. CHAPTER VI Linear Algebraic Groups in the 20th Century The interest in linear algebraic groups was revived in the 1940s by C. Chevalley and E. Kolchin. The most salient features of their contributions are outlined in Chapter VII and VIII. Even though they are put there to suit the broader context, I shall as a rule refer to those chapters, rather than repeat their contents. Some of it will be recalled, however, mainly to round out a narrative which will also take into account, more than there, the work of other authors. §1. Linear algebraic groups in characteristic zero. Replicas 1.1. As we saw in Chapter V, §4, Ludwig Maurer thoroughly analyzed the properties of the Lie algebra of a complex linear algebraic group. This was Cheval ey's starting point. -
Sir Michael Atiyah the ASIAN JOURNAL of MATHEMATICS
.'•V'pXi'iMfA Sir Michael Atiyah THE ASIAN JOURNAL OF MATHEMATICS Editors-in-Chief Shing-Tung Yau, Harvard University Raymond H. Chan, Chinese University of Hong Kong Editorial Board Richard Brent, Oxford University Ching-Li Chai, University of Pennsylvania Tony F. Chan, University of California, Los Angeles Shiu-Yuen Cheng, Hong Kong University of Science and Technology John Coates, Cambridge University Ding-Zhu Du, University of Minnesota Kenji Fulcaya, Kyoto University Hillel Furstenberg, Hebrew University of Jerusalem Jia-Xing Hong, Fudan University Thomas Kailath, Stanford University Masaki Kashiwara, Kyoto University Ka-Sing Lau, Chinese University of Hong Kong Jun Li, Stanford University Chang-Shou Lin, National Chung Cheng University Xiao-Song Lin, University of California, Riverside Raman Parimala, Tata Institute of Fundamental Research Duong H. Phong, Columbia University Gopal Prasad, Michigan University Hyam Rubinstein, University of Melbourne Kyoji Saito, Kyoto University Jalal Shatah, Courant Institute of Mathematical Sciences Saharon Shelah, Hebrew University of Jerusalem Leon Simon, Stanford University Vasudevan Srinivas, Tata Institue of Fundamental Research Srinivasa Varadhan, Courant Institute of Mathematical Sciences Vladimir Voevodsky, Northwestern University Jeff Xia, Northwestern University Zhou-Ping Xin, Courant Institute of Mathematical Sciences Horng-Tzer Yau, Courant Institute of Mathematical Sciences Mathematics in the Asian region has grown tremendously in recent years. The Asian Journal of Mathematics (ISSN 1093-6106), from International Press, provides a forum for these developments, and aims to stimulate mathematical research in the Asian region. It publishes original research papers and survey articles in all areas of pure mathematics, and theoretical applied mathematics. High standards will be applied in evaluating submitted manuscripts, and the entire editorial board must approve the acceptance of any paper. -
2,3,T)-Generations for the Tits Simple Group 2F4(2
2 0 (2; 3; t)-Generations for the Tits simple group F4(2) MOHAMMED ALI FAYA IBRAHIM FARYAD ALI King Khalid University King Khalid University Department of Mathematics Department of Mathematics P.O. Box 9004, Abha P.O. Box 9004, Abha SAUDI ARABIA SAUDI ARABIA mafi[email protected] [email protected] Abstract: A group G is said to be (2; 3; t)-generated if it can be generated by two elements x and y such that o(x) = 2, o(y) = 3 and o(xy) = t. In this paper, we determine (2; 3; t)-generations of the Tits simple group ∼ 2 0 T = F4(2) where t is divisor of jTj. Most of the computations were carried out with the aid of computer algebra system GAP [17]. 2 0 Key–Words: Tits group F4(2) , simple group, (2; 3; t)-generation, generator. 1 Introduction was first determined by Tchakerian [19]. Later but independently, Wilson [20] also determined the max- A group G is called (2; 3; t)-generated if it can be gen- imal subgroups of the simple group T, while studying erated by an involution x and an element y of order 3 the geometry of the simple groups of Tits and Rud- such that o(xy) = t. The (2; 3)-generation problem valis. has attracted a vide attention of group theorists. One For basic properties of the Tits group T and infor- reason is that (2; 3)-generated groups are homomor- mation on its subgroups the reader is referred to [20], phic images of the modular group P SL(2; Z), which [19]. -
GROUPS of OUTER TYPE E6 with TRIVIAL TITS ALGEBRAS This
GROUPS OF OUTER TYPE E6 WITH TRIVIAL TITS ALGEBRAS SKIP GARIBALDI AND HOLGER P. PETERSSON Abstract. In two 1966 papers, J. Tits gave a construction of excep- tional Lie algebras (hence implicitly exceptional algebraic groups) and a classification of possible indexes of simple algebraic groups. For the special case of his construction that gives groups of type E6, we connect the two papers by answering the question: Given an Albert algebra A and a separable quadratic field extension K, what is the index of the resulting algebraic group? This article links two 1966 papers by Jacques Tits—namely, [Ti 66a] and [Ti 66b]—concerning simple linear algebraic groups over a field k. In the first paper, he gave a construction that takes a composition algebra K and a degree 3 Jordan algebra A and produces a simple algebraic group G(A, K). The Killing-Cartan type of the resulting group is given by the famous magic square: dim A 1 3 6 9 15 27 1 A1 A2 C3 F4 dim K 2 A2 A2 × A2 A5 E6 4 A1 A1 × A1 × A1 C3 A5 D6 E7 8 G2 D4 F4 E6 E7 E8 In the second paper, he listed the possible indexes of a simple linear algebraic group. Recall from [Ti 66b, 2.3] that the index is the Dynkin diagram embellished so as to describe a maximal k-split torus and the action of the absolute Galois group on the Dynkin diagram. The question (0.1) What is the index of the group G(A, K)? gives a natural link between the two papers. -
On the Characters of Affine Kac–Moody Groups
Proceedings of the Edinburgh Mathematical Society (1993) 36, 179-195 © ON THE CHARACTERS OF AFFINE KAC-MOODY GROUPS by STEPHEN SLEBARSKI (Received 18th October 1990, revised 17th March 1992) Let G be an affine Kac-Moody group over C, and V an integrable simple quotient of a Verma module for g. Let Cmm be the subgroup of G generated by the maximal algebraic torus T, and the real root subgroups. It is shown that <5eO'™ (the least positive imaginary root) gives a character (5eHom(G,C) such that the pointwise character xa of V may be defined on Gmi° r\ G>1. 1980 Mathematics subject classification: 17B67, 22E67. 0. Introduction A Kac-Moody group G over C, is associated to a pair (A, hz) where A is a generalized, indecomposable, Cartan nxn matrix of rank /, and hz is a free Z-module such that n — / = rank hz —n. Then G has a (B,N) pair forming a Tits system with Weyl group W=N/(BnN) (see also [12, 4, 9]). The Lie algebra g of G has a root space decomposition, and it is required that the im roots O£Hom(hz,Z) = :h|. We have O = <D" u O , where <&" is the W orbit of the simple roots and <t>im = O\Ore. If G is affine (that is A is symmetrizable, positive semidefinite) then there is an 1 analytic construction as a loop group [3]. Take a central extension S -*L.K(0)->LK{0) of l the loop group of a compact, connected almost simple Lie group Km by the circle S (this is obtained [8] from a closed, left invariant integral 2-form on LKm, if Ko is simply connected). -
Moonshines for L2(11) and M12
Moonshines for L2(11) and M12 Suresh Govindarajan Department of Physics Indian Institute of Technology Madras (Work done with my student Sutapa Samanta) Talk at the Workshop on Modular Forms and Black Holes @NISER, Bhubaneswar on January 13. 2017 Plan Introduction Some finite group theory Moonshine BKM Lie superalgebras Introduction Classification of Finite Simple Groups Every finite simple group is isomorphic to one of the following groups: (Source: Wikipedia) I A cyclic group with prime order; I An alternating group of degree at least 5; I A simple group of Lie type, including both I the classical Lie groups, namely the groups of projective special linear, unitary, symplectic, or orthogonal transformations over a finite field; I the exceptional and twisted groups of Lie type (including the Tits group which is not strictly a group of Lie type). I The 26 sporadic simple groups. The classification was completed in 2004 when Aschbacher and Smith filled the last gap (`the quasi-thin case') in the proof. Fun Reading: Symmetry and the Monster by Mark Ronan The sporadic simple groups I the Mathieu groups: M11, M12, M22, M23, M24; (found in 1861) I the Janko groups: J1, J2, J3, J4; (others 1965-1980) I the Conway groups; Co1, Co2, Co3; 0 I the Fischer groups; Fi22. Fi23, Fi24; I the Higman-Sims group; HS I the McLaughlin group: McL I the Held group: He; I the Rudvalis group Ru; I the Suzuki sporadic group: Suz; 0 I the O'Nan group: O N; I Harada-Norton group: HN; I the Lyons group: Ly; I the Thompson group: Th; I the baby Monster group: B and Sources: Wikipedia and Mark Ronan I the Fischer-Griess Monster group: M Monstrous Moonshine Conjectures I The j-function has the followed q-series: (q = exp(2πiτ)) j(τ)−744 = q−1+[196883+1] q+[21296876+196883+1] q2+··· I McKay observed that 196883 and 21296876 are the dimensions of the two smallest irreps of the Monster group.