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

Quark lepton symmetry

  1. Feb 3, 2014 #1
    If I understand correctly, conservation of baryon and lepton numbers imply that quarks and leptons are "basic" i.e. non-interchangeable particles? What happens when one such particle is annihilated, can the energy produced be used to "generate" the other type, or do some additional particles always "carry away" the baryonness or leptonness? In a grand unification of the strong and electroweak forces, would it not require a new symmetry that does allow these particles to interconvert, i.e. a failure of conservation of those numbers? Is that the presumed mode of a spontaneous proton decay, the thing everyone has looked for unsuccessfully so far?

    If this topic has been discussed previously please direct me to the relevant post. I tried a text search but could not find something exactly appropriate. Thanks!
  2. jcsd
  3. Feb 3, 2014 #2


    User Avatar
    Science Advisor

    Annihilation is the result of a particle meeting its antiparticle, so the net number is unchanged. The result is typical a pair of photons, which could then become something else, still preserving the count.
  4. Feb 3, 2014 #3
    Of course, that makes perfect sense. I wasn't thinking mechanistically enough about the process. What about lepton/quark symmetry and interconversion, are these implicit in strong/electroweak unification theories?

  5. Feb 3, 2014 #4
    Such processes are theoretically possible non-perturbatively even in the Standard Model, but only at extreme high energies, and have not been experimentally observed I believe. But yeah GUT models usually have such processes, and it can be a problem that they occur too easily, so that some extra reason may be needed to forbid them so that, as you say, protons don't decay too fast.
  6. Mar 22, 2014 #5
    the process particle anti-particle have not any quantum number (total color or lepton...these are zero in the initial state), therefore the initial state can becomes through some process in another two particles, which in principle can be different in color, lepton quantum numbers. The only condition is that the final two or three ....final state also have not any quantum number.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook