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The weak force and effective coupling

  1. May 20, 2010 #1
    I just read something about the creation of deuteron in the first step of the pp cycle. Given that you have the reaction: p + p -> d + e^+ + v_e, where e^+ is a positron and v_e is an electron neutrino. Since there is a neutrino present, it is a weak interaction. In addition, as the interaction is weak (and at low energies?) the effective coupling is small.

    My question is, do weak interactions only proceed at low energies? I have read about 'low energy limits' and how this means only virtual W's can be made. How is it then that this process can proceed at roughly 1.5 x 10^7 K in the Sun's core?
  2. jcsd
  3. May 20, 2010 #2
    Weak interactions in generally occur most readily at energies where the intermediate gauge boson is very close to its mass shell (about 80 GeV for the W and 90 GeV for the Z). However, at that kind of energy the nucleons involved tend to fragment, so you wouldn't get deuterium.

    Also, not that 1.5 x 10^7 K does not get you to terribly high energy. It only amounts to an avererage of 1.3 keV kinetic energy per proton, which is, as these things go, rather low energy. (Remember, the electron's mass is 511 keV and the proton's is 938 MeV.)
  4. May 20, 2010 #3
    Okay then, so weak interactions don't really proceed at low energies? (i am not too sure what the ideal energies are for strong interactions).
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