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

I Energy conservation concerns in the weak interaction

  1. Aug 15, 2017 #1
    I have a few questions:

    Can a u quark turn into a d quark (heavier) via the weak interaction? If so, how is the mass/energy shortfall made up?

    How can the (supermassive) carrier bosons (W, Z) be called into being? Where does the energy come from? Or is the energy bill unpaid because they are virtual particles, on the verge of existence? Is it akin to a tunneling effect?

    Thank you.
     
  2. jcsd
  3. Aug 15, 2017 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Quarks don't exist as isolated objects. There is no u->d process without "context".
    In radioactive decays: They don't. There are just virtual W, not real particles.
    In particle accelerators: We give the particles enough energy.
     
  4. Aug 16, 2017 #3
    The context is within a nucleon in a nucleus, e.g. electron capture.
     
  5. Aug 16, 2017 #4
    Thank you. I already had that. I guess I could just write "they are not real" but that seems to me an unsatisfactory explanation. What is meant by a virtual particle? Is it just an arbitrary expedient, like when explaining lightning saying "Thor does it"? There has to be something more to be said.
     
  6. Aug 16, 2017 #5
    A proton turning into neutron is caused by one u quark turning into d quark. And a neutron is heavier.
    The mass/energy shortfall is made up by the (larger) binding energy of the neutron/d quark.
    Yes, tunnelling is a good comparison for virtual particles.
     
  7. Aug 16, 2017 #6
    Thank you Snorkack!

    If nobody contradicts, I may be onto something here.
     
  8. Aug 16, 2017 #7

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    A mathematical concept in perturbation theory, which is a tool to calculate approximations to processes.
    It is not "Thor does it", because we can calculate how often what happens.
    Then it can be possible, it depends on the nucleus and the binding energy of the initial and potential final nucleus.
     
  9. Aug 16, 2017 #8
    I am not sure that
    For the simplest example of what a virtual particle is, consider virtual photon.
    Electromagnetic field includes electromagnetic waves. They are freely propagating, carry energy, momentum and angular momentum independent of the source and eventual recipient.
    They are also observably quantized into real photons.
    But not all electromagnetic field is free waves.
    Electromagnetic field also includes electrostatic and magnetostatic fields.
    As well as evanescent waves. Oscillating electric fields exist in directions and volumes of space into which they are not freely propagating.
    The concept of "virtual particle" is based on the idea of treating unfree fields as quantized like the freely propagating waves are.
    If you look at the electrostatic field of a point charge, you can define the total strength of the field lines included. But can you break down the electrostatic field of a point charge into a countable number of virtual photons, the way you can in theory count the radio wave real photons emitted by an antenna?
     
  10. Aug 16, 2017 #9

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    No.

    How is your post related to the part you quoted?
    "How often what happens" is about physical processes, e. g. decays, cross sections and so on.
     
  11. Aug 17, 2017 #10
    Ah, the real final outcome?
    But do you need virtual particles for that?
     
  12. Aug 17, 2017 #11

    vanhees71

    User Avatar
    Science Advisor
    2016 Award

    To make it very clear: "Virtual particles" is a confusing buzzword for propagators in Feynman diagrams, depicted there by internal lines. They are not interpretable as particles at all. That's only possible in the sense of asymptotic free states, and sometimes even those are not as simple as it looks in the standard procedure idealizing them to free plane-wave states. For a full understanding you have to study relativistic quantum field theory and deal with pretty mind-boggling conceptual problems, related to the definition of asymptotic states, LSZ reduction (named after Lehmann, Symanzik, and Zimmermann), and all that.
     
  13. Aug 17, 2017 #12

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    No, there are calculation methods that do not have virtual particles. Lattice calculations for example.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Energy conservation concerns in the weak interaction
  1. Weak interaction (Replies: 4)

  2. Weak interaction (Replies: 3)

  3. Weak Interactions (Replies: 5)

Loading...