How does Wu-Ki Tung use Euler angles to get these results in group theory?

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This identity is known as the Baker-Campbell-Hausdorff formula. Using this formula, you can expand the exponentials in the equations and simplify them to get the desired results. In summary, the author uses the Baker-Campbell-Hausdorff formula to expand the exponentials and simplify the equations, resulting in the equations R^{-1} J_3 R and e^{i \gamma J_3}J_2 e^{-i \gamma J_3}.
  • #1
Phymath
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In a book about group theory in physics (Wu-Ki Tung) he is using the Euler angle representation of a rotation I'm unsure how he gets the following results...

[tex] R(\alpha,\beta,\gamma) = e^{-i \alpha J_z}e^{-i \beta J_y}e^{-i \gamma J_z}[/tex]

he writes

[tex] R^{-1} J_3 R = -sin \beta (J_+ e^{i \gamma} + J_ e^{-i \gamma})/2 + J_3 cos \beta [/tex]
and
[tex] e^{i \gamma J_3}J_2 e^{-i \gamma J_3} = i[-J_+ e^{i \gamma} + J_- e^{-i \gamma}]/2 [/tex]

how in the world is he getting this!? [tex] J_2 = (J_+ - J_-)/2i [/tex] i know that must be used but how is he getting this?! I tried doing a long expansion of all the exponentials in a taylor series but that didnt get me anywhere. Any help would be aweosme (you can also find this book in google books the page this is on is p.141 Group theory in Physics Wu-ki Tung) Thanks to anyone
 
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  • #2
You can use the following identity.

[itex]e^{A}Be^{-A}=B+[A,B]+\frac{1}{2!}[A,[A,B]]+\frac{1}{3!}[A,[A,[A,B]]]+...[/itex]
 

FAQ: How does Wu-Ki Tung use Euler angles to get these results in group theory?

1. What is Group QM?

Group QM stands for Group Quantum Mechanics. It is a mathematical framework used to study the behavior of particles at the quantum level when they are in groups or interacting with each other.

2. How is Group QM different from traditional QM?

In traditional quantum mechanics, the focus is on the behavior of individual particles. In Group QM, the focus is on the collective behavior of groups of particles and their interactions with each other.

3. What are some applications of Group QM?

Group QM has many applications in fields such as condensed matter physics, chemistry, and materials science. It is also used in studying complex systems, quantum computing, and quantum information theory.

4. What are some challenges in studying Group QM?

One of the main challenges in studying Group QM is the complexity of the mathematical equations involved. It also requires a deep understanding of traditional QM and advanced mathematical concepts such as group theory and representation theory.

5. How does Group QM relate to other branches of physics?

Group QM is closely related to other branches of physics, such as classical mechanics, statistical mechanics, and quantum field theory. It provides a framework for understanding the behavior of particles in groups, which is essential in many areas of physics.

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