18.745 | Fall 2020 | Graduate

Lie Groups and Lie Algebras I

Pages

Lecture 1: Manifolds

Lecture 2: Lie Groups I

Lecture 3: Lie Groups II

Lecture 4: Homogeneous Spaces and Lie Group Actions

Problem set 1 due

Lecture 5: Tensor Fields

Lecture 6: Classical Lie Groups

Problem set 2 due

Lecture 7: The Exponential Map of a Lie Group

Lecture 8: Lie Algebras

Problem set 3 due

Lecture 9: Fundamental Theorems of Lie Theory

Lecture 10: Proofs of the Fundamental Theorems of Lie Theory

Problem set 4 due

Lecture 11: Representations of Lie Groups and Lie Algebras

Lecture 12: The Universal Enveloping Algebra of a Lie Algebra

Problem set 5 due

Lecture 13: The Poincare-Birkhoff-Witt Theorem

Lecture 14: Free Lie Algebras and the Baker-Campbell-Hausdor Formula

Problem set 6 due

Lecture 15: Solvable and Nilpotent Lie Algebras and Theorems of Lie and Engel

Lecture 16: Semisimple and Reductive Lie Algebras, the Cartan Criteria

Problem set 7 due

Lecture 17: Proofs of the Cartan Criteria and Properties of Semisimple Lie Algebras

Lecture 18: Extensions of Representations, Whitehead’s Theorem, and Compete Reducibility

Problem set 8 due

Lecture 19: Structure of Semisimple Lie Algebras I

Lecture 20: Structure of Semisimple Lie Algebras II

Problem set 9 due

Lecture 21: Root Systems

Lecture 22: Properties of the Weyl Group

Problem set 10 due

Lecture 23: Dynkin Diagrams

Lecture 24: Construction of a Semisimple Lie Algebra from a Dynkin Diagram

Problem set 11 due

Lecture 25: Representation Theory of Semisimple Lie Algebras

Lecture 26: The Weyl Character Formula

Problem set 12 due

[LN] = Lecture Notes

[K] = Alexander Kirillov Jr.’s An Introduction to Lie Groups and Lie Algebras.

Use Problem sets (PDF) to complete the problems assigned below.

Homework 1: K 2.1–2.6       
Additional Exercises 1: LN 1.10

Homework 2: K 2.7–2.16       
Additional Exercises 2: LN 3.4, 3.6, and 3.9

Homework 3: LN 6.2, 6.4, 6.5, and 6.14–6.17        
Additional Exercises 3: LN 6.1, 6.9, and 6.11  

Homework 4: K 3.1, 3.5–3.9, and 3.11         
Additional Exercises 4: LN 3.12 and 4.3

Homework 5: K 3.13, and 3.15–3.19        
Additional Exercises 5: LN 5.7 and 5.11

Homework 6: K 4.2, 4.4, 4.7 and 4.9        
Additional Exercises 6: LN 7.7 and 8.11 

Homework 7: K 4.1, 4.11, 4.12, and 5.1–5.7            
Additional Exercises 7: LN 9.2 and 9.17

Homework 8: K 6.1–6.6; LN 11.19, 12.7, 15.2, and 15.5         
Additional Exercises 8: LN 14.15 and 15.7

Homework 9: LN 11.4, 11.20, 15.11, and 15.16        
Additional Exercises 9: LN 16.13 and 18.3

Homework 10: K 7.1, 7.2, 7.4, 7.5, and 7.8–7.11         
Additional Exercises 10: LN 22.4

Homework 11: K 7.7, and 7.12–7.16         
Additional Exercises 11: LN 22.18

Homework 12: LN 23.9, 23.10, 23.12, and 23.13          
Additional Exercises 12: LN 23.16, 23.17, and 26.7

Course Meeting Times

Lectures: 2 sessions / week, 80 minutes / session

Prerequisites

Course Overview

We will discuss both Lie algebras and Lie groups together in both halves. (These subjects are so intimately related that it is more natural to study them together.) But still the first semester will be mostly algebra while the second one will involve a bit more geometry and analysis. There will be a lot of emphasis on examples.

In the first half (18.745) we will essentially follow Alexander Kirillov Jr.’s An Introduction to Lie Groups and Lie Algebras (PDF), excluding the more advanced material on representations of Lie groups (such as Haar measure, Peter-Weyl theorem, etc.), but with more detailed treatment of Lie algebras. Namely, chapters 2 and 3 (without proofs of the harder theorems, such as Lie’s third theorem), 4.1 to 4.4, and chapters 5 to 8, classification of simple complex Lie algebras with proof. The course also discusses universal enveloping algebras, the Poincare-Birkhoff-Witt theorem, free Lie algebras, and the Campbell-Hausdorff formula.

In the second half (18.755) we will give a more in-depth treatment of Lie groups (relying on what was done in the first half). Topics will include representations of GL(n) and other classical groups; fundamental and minuscule representations; applications of representation theory of Lie groups to quantum mechanics of the hydrogen atom; Haar measure and integration on compact groups; representations of compact (in particular, finite) groups; the Peter-Weyl theorem with proof; maximal tori in compact Lie groups; complex reductive Lie groups; Borel and parabolic subgroups; flag variety; classification of real reductive groups and their structure (maximal tori, maximal compact subgroups, Cartan and Iwasawa decompositions); cohomology of Lie groups and Lie algebras; classification of finite-dimensional simple complex Lie algebras with proof; Levi decomposition; proofs of the third fundamental theorem of Lie theory; Ado’s theorem.

Assignments

Homework will be assigned weekly (first one after 1 week of class) and due in one week. It contains a lot of important material.

Grading

The grade will be given solely on the basis of homework.

Course Info

Instructor
Departments
As Taught In
Fall 2020
Level
Learning Resource Types
Lecture Notes
Problem Sets