Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Representation Theory and Particle Theory

  1. Jan 21, 2012 #1
    I am familiar with the representation theory of finite groups and Lie groups/algebra from the mathematical perspective, and I am wondering how quantum mechanics/quantum field theory uses concepts from representation theory. I have seen the theory of angular momentum in quantum mechanics, and I realized that Lx, Ly, and Lz, the components of angular momentum, are elements of the Lie algebra SO(3). I also heard of the notion that irreducible representations correspond with elementary particles and that the Casimir element can measure scalar quantities such as mass. Unfortunately, my knowledge in this area is merely a bunch of scattered facts. Could anyone explain the foundations of the relationship between representation theory and quantum physics, or provide a resource (book or website) that explains this connection? Thanks.
  2. jcsd
  3. Jan 21, 2012 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

  4. Jan 21, 2012 #3
    I would recommend the second chapter of Weinberg's Quantum theory of Fields, he does construct the particle states from the irreducible representations of the Lorentz Group.
  5. Jan 21, 2012 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The best place I know to read about particles and irreducible representations is chapter 2 of Weinberg's QFT book. I'm not saying that it's great, only that it's not bad for a physics book, and that I don't know a better place. Link

    Edit: D'oh. Too slow again.
  6. Jan 21, 2012 #5
    Yep, burned ;)
  7. Jan 22, 2012 #6
    Ballentine has some discussion of irreducible representations (although he doesn't use that term) and their role in QM.

    BTW, I have the opposite problem. I have a general idea about the role of Lie groups in QM, but I'd like to learn some math: representation of finite groups, semisimplicity, irreps, and then once I've mastered that stuff Lie groups and Lie algebras. Does anyone know of a good intro to that kind of material, something accessible to me having only taken a standard undergrad abstract algebra course?
  8. Jan 22, 2012 #7
    That's pretty interesting...how did you manage to understand its role within - and connection to - QM if you didn't know the mathematics of group & representation theory ? I am trying to self-study this area at the moment ( I'm not a scientist by trade ), but am finding it hard going.
  9. Jan 22, 2012 #8
    Shouldn't be hard to find what you are looking for, a lot of group theory books start by introducing the representation theory and its concepts before going to the special case of Lie Groups, one example:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook