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Need simple SUSY explanation

  1. May 2, 2009 #1
    1. The problem statement, all variables and given/known data
    I am giving a short talk on supersymmetry for my intro to high energy class, but I do not have the time to read an entire book on the subject. Most resources I have found go into much more depth than I need, but these seem to be the only resources. Can anyone help me with the basics conceptually?


    2. Relevant equations

    N/A

    3. The attempt at a solution

    Here's what I already know:

    SUSY attempts to explain certain problems with the standard model, namely the fact that the forces do not have the same strengths at any energy, and the fact that the masses of the particles, or more directly the Higgs' boson, are far different from their theoretical values (due to renormalization problems of the Higgs mass).

    The fact that fermions could be related to bosons is due to the fact that when the corrections to the Higgs mass are calculated, the divergent quantities seem to cancel if both fermionic as well as bosonic contributions to the correction are included. This means that the Higgs' mass is a result of its fermionic nature as well as its bosonic nature. Since other particle masses are calculated from the Higgs mass, all particles should share this symmetry.

    My questions are:

    Why does this imply that no known particles are superpartners of each other (e.g. why are the known fermions not superpartners for any of the known bosons)?

    How does this affect the unification of the forces? I read somewhere that without SUSY, the forces never actually converge to a single energy, but with it they do. I do not understand this.

    Finally, how does the prediction of the spin-2 graviton come about?

    I understand that this is a very complex topic and that a lot of intense group theory is needed to fully understand it, but any help would be extremely appreciated. Thanks so much in advance!!
     
  2. jcsd
  3. May 3, 2009 #2

    malawi_glenn

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    Science Advisor
    Homework Helper

    SUSY is more than this, it is a symmetry of space-and time in a whole new way and that imposes a symmetry between fermion fields and scalar-fields.

    answers to Q's:

    i) superpartners should have equal mass is SUSY is exact and also same charge etc, the known bosons we have is Z and the W's, why they are not superpartners to say the electron is trivially shown. Also one has to turn the argument around, why SHOULD the Z boson for instance be superpartner to the muon?

    ii) The strength of the force depends on a special parameter in the lagrangian, the coupling constant, and this constant is not a constant but depends on energy. As you know, in our daily life here electromagnetism seems to be the strongest force, but when we go to higher energies, the strong force is.. and so on. The weak force and EM can be unified to one single force at some quite high energy scale, this has been shown and noble prize was awarded for that. And this is done since these coupling constants meet in one point. But the strong, weak and EM does not meet at one point, thus seemingly pointless to make a unification of those 3 into 1. But with susy, this is possible, they can meet in one point.

    iii) I think that would be too technical for you to understand... the graviton is not even SUSY (the gravitino is), but anyway, the carrier of the gravitational force must be a rank-2 tensor, i.e transform as a an object with spin 2.

    group theory is just the beginning...
     
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