Rational Representations of Algebraic Groups Tensor Products and Fil

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1140 Stephen Donkin

Rational Representations of Algebraic Groups: Tensor Products and Filtrations

Springer-Verlag Berlin Heidelberg New York Tokyo

Author

Stephen Donkin School of Mathematical Sciences, Queen Mary College Mile End Road London E1 4NS, England

Mathematics Subject Classification (1980): 20G ISBN 3-540-15668-2 Springer-Verlag Berlin Heidelberg New York Tokyo ISBN 0-387-15668-2 Springer-Verlag New York Heidelberg Berlin Tokyo This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translating, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to "Verwertungsgesellschaft Wort", Munich.

© by Springer-Verlag Berlin Heidelberg 1985 Printed in Germany Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr. 2146/3140-543210

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Table of Contents

Introduction

1

Homological algebra

7

1.1

Induction

7

Chapter 1.

1.2

Injective modules for soluble groups

12

1.3

Reductive groups

14

1.4

B cohomology

15

1.5

Induced modules

16

1.6

Kempf's Vanishing Theorem

18

1.7

Parabolic subgroups

18

More homological algebra

21

Chapter 2. 2.1

Applications of the Vanishing Theorem

21

2.2

Euler characteristics

22

2.3

Some useful results

26

Reductions

31

Good filtrations

31

Chapter 3. 3.1 3.2

Good filtrations for reductive groups

35

3.3

Canonical filtration

38

3.4

Good filtrations for semisimple groups

40

3.5

Good filtrations for sernisimple, simply connected groups

46

3.6

The canonical filtration revisited

49

3.7

A useful lemma

50

The classical groups

52

Exterior powers

52

Chapter 4. 4.1 4.2

Miniscule weights

53

4.3

Exceptional weights

53

4.4

The first fundamental dominant weight

54

VI

4.5

Some module homomorphisms

56

4.6

Character formulas

57

4.7

The canonical filtration again

59

4.8

The restriction of Y(A to P Q r) The restriction of Y(A ) to the maximal parabolic subgroups r

60

Homological algebra revisited

76

4.9

Chapter 5.

70

Chapter 6.

86

Chapter 7.

89

Introduction

89

7.2

Y (AI)

89

7.3

Y (A

7.4

Odd characteristic

7.5

Exact sequences

7.6 7.7

The restriction of Y(A ) to P Q 2 M, N/E and Y /S

7.8

l:

,',\ {a 3}

110

7.9

l:

,',\{a }

112

7.10

l:

117

7.11

,',\{a } l

l: arbitrary

124

7.12

Y(A

124

7.1

92

4)

98

99

2

7.13

Y(A

2)

and

2)

109

128

are true

Chapter 8.

Chapter 9.

101

133

E

140

7

9.1

Y (AI)

140

9.2

Y (A

142

9.3

6) p '" 2 or 7

9.4

The restriction of Y(A

9.5 9.6 9.7 9.8

.

P"

143

7)

to P

n

147

(D)

155

Character formulas

157

L.

.

P" t..

Y (A

7

)

(E)

160 168

VII

Chapter 10. 10.1

E

169

8

169

Y (AI)

10.2

p

10.3

The restriction of Y (1.. ) to P 7 n · PL (D)

178

Orbits and characters · PL (E)

187

10.4 10.5 10.6 10.7

;