I am currently looking for an introductory text on Lie groups and Lie algebras with an emphasis on differential geometry. (I already have a little bit of background knowledge on smooth manifolds, having read through a fair amount of John M. Lee's Introduction to Smooth Manifolds.) After some searching online I found these three textbooks:
- Sigurdur Helgason, Differential Geometry, Lie Groups, and Symmetric Spaces
- V. S. Varadarajan, Lie Groups, Lie Algebras, and Their Representations
- Anthony W. Knapp, Lie Groups Beyond an Introduction
I've heard that Knapp may be too advanced for an introductory textbook. I would also be open to any other suggestions.