Adjoint representation of SU(2)

In summary, the conversation discusses the use of ad(x)y = [x,y] and Ad(X) = gXg^-1 in finding ad(S1) and X, and the connection between ad and Ad through matrix exponentiation. The speaker mentions their previous articles on SU(2) representations and asks for help in solving Ad(expX) = exp(ad(X)) for the matrices calculated. The other person suggests starting with simpler Lie groups and using differentiation of curves to show the connection.
  • #1
nigelscott
135
4

Homework Statement


[/B]
I am looking at this document. http://www.math.columbia.edu/~woit/notes3.pdf

Homework Equations


[/B]
ad(x)y = [x,y]

Ad(X) = gXg-1

The Attempt at a Solution


[/B]
I understand how ad(S1) and X is found but I don't understand what g and g-1 to use to find Ad(X). Also I need to show that ad and Ad are connected via matrix exponentiation.
 
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  • #2
To be honest, I don't really want to read four pages to answer a possibly simple question, the more as I've already written two insight articles, which deal with ##SU(2)## representations. I worked out quite a few explicit formulas for expressions in certain bases. So maybe you'll find there what you are looking for (you can skip the first two sections).

https://www.physicsforums.com/insights/journey-manifold-su2mathbbc-part/
https://www.physicsforums.com/insights/journey-manifold-su2-part-ii/
 
  • #3
Thanks. I worked through your paper and understand how you got to part 2 (12) and (13). The part 1 am stuck on now is solving Ad(expX) = exp(ad(X)) for the matrices you have calculated. When I try to calculate the matrix exponential I get strange results. Any pointers you could give would be of great help. Thanks again.
 
  • #4
nigelscott said:
When I try to calculate the matrix exponential I get strange results. Any pointers you could give would be of great help.
It's not really funny to calculate the exponentials of ##(3\times 3)-##matrices and easy to make mistakes. I guess, that's why I haven't really seen it anywhere. I would start with ##(2\times 2)-##matrices and the Lie group of matrices of the form ##\begin{bmatrix}a&b\\0&0\end{bmatrix}## with ##a \neq 0## and the Lie algebra ##[X,Y]=Y## which is easier than with simple Lie groups which have entries on both sides of the diagonal. It's also the reason why I used the differentiation of curves in the Lie group to show the connection to its Lie algebra. Exponentiation is basically the way back, an integration.
 

Related to Adjoint representation of SU(2)

1. What is the adjoint representation of SU(2)?

The adjoint representation of SU(2) is a mathematical concept used in the study of group theory and quantum mechanics. It refers to the linear transformation that maps the group elements of SU(2) onto themselves.

2. How is the adjoint representation of SU(2) related to the Lie algebra?

The adjoint representation of SU(2) is closely related to the Lie algebra of the group. It is a faithful representation, meaning that it preserves the structure and properties of the group. In other words, the Lie algebra can be derived from the adjoint representation.

3. What is the significance of the adjoint representation of SU(2) in physics?

The adjoint representation of SU(2) has many applications in physics, particularly in the study of quantum mechanics and particle physics. It is used to describe the symmetries and transformations of physical systems, such as the spin of particles.

4. How is the adjoint representation of SU(2) different from the fundamental representation?

The fundamental representation of SU(2) is a 2-dimensional representation that describes the spin-1/2 particles. In contrast, the adjoint representation is a 3-dimensional representation that describes the interactions between particles and their symmetries.

5. Can the adjoint representation of SU(2) be extended to other groups?

Yes, the concept of the adjoint representation can be extended to other groups, such as SU(N) and SO(N). However, the specific properties and equations may differ for each group, as they have different Lie algebras and representations.

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