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B Weak fields, higgs fields.. forces

  1. Aug 4, 2016 #1
    Why is the weak field a force of nature.. while the higgs field is not a force of nature.. what is the signature or things to look for before a field can be considered as a force of nature?
     
  2. jcsd
  3. Aug 5, 2016 #2

    Orodruin

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    What is referred to as "forces of nature" in popular litterature are gauge fields. These fields relate to fundamental symmetries of the theory. The Higgs field is not s gauge field. In fact, it breaks some of the mentioned symmetries, which is the reason the W and Z have mass. After symmetry breaking, three of four degrees of freedom in the Higgs field are eaten by the W and Z whfn they become massive. In some sense, the Higgs field therefore is part of the weak force.
     
  4. Aug 5, 2016 #3
    Are 100% of fields part of the quantum vacuum (or since the quantum vacuum is one which has the lowest (energetic) ground state.. should the question instead be "are 100% of fields part of the quantum field?)? But gravitational field doesn't appear to be part of the quantum vacuum (or quantum field?). Are there other fields not part of the quantum vacuum (fields?)?
     
  5. Aug 5, 2016 #4

    mfb

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    What do you mean by "part of the quantum vacuum"? All fields have a value everywhere in the vacuum, typically zero (that's the point of having a vacuum), the Higgs field is an exception.

    We don't know how to quantize gravity properly yet, and the existing approaches would be beyond the scope of this thread I think.
     
  6. Aug 5, 2016 #5
    Ok. Are all kinds of quantum fields related to the forces of nature? (Orodruin stated the higgs field is part of the weak force)
    Are there any quantum fields that are not related to the forces of nature?
     
  7. Aug 5, 2016 #6

    mfb

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    Most of them are related to what we typically call particles: electrons, muons, tau, quarks and neutrinos.
     
  8. Aug 9, 2016 #7
    I know the Quantum Vacuum is the lowest energetic (ground) state of a quantum system
    But is it right to say the Vacuum is the source of the quantum fields?
    Isn't it the quantum fields is its own origin and there is no vacuum that produced it.
    Then when many authors especially pop-sci authors state the vacuum produce the quantum fields.. then it is not exactly correct?
     
  9. Aug 10, 2016 #8

    mfb

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    I don't think that is a useful approach.
    I don't think that is useful either.

    The fields just exist. They are not "produced" by anything.
     
  10. Aug 10, 2016 #9
    Therefore what I mentioned is right that "quantum fields is its own origin and there is no vacuum that produced it". Why do you say the statement is not useful either?
     
  11. Aug 10, 2016 #10

    mfb

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    "is its own origin" looks like something would produce something.
     
  12. Aug 10, 2016 #11
    In the above, why did you mention "All fields have a value everywhere in the vacuum".. isn't it "vacuum" has no place in quantum field theory.. there are only quantum fields and quantum vacuum is just the ground state of it.. there is really no "vacuum". What is the correct usage of the word "vacuum" in QFT (if it's valid at all).
     
  13. Aug 10, 2016 #12

    mfb

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    There is spacetime with fields in it. If all those fields are in the lowest energy state, we call this vacuum. You can call it "quantum vacuum" if you want to highlight that you work with quantum field theory, but it is the same vacuum as in classical mechanics, it is just described with different concepts.
     
  14. Aug 10, 2016 #13
    But classical mechanics are just coarse graining of quantum reality. So how could there still be classical mechanics like the vacuum. In the universe, there are only quantum fields and general relativitistic geometry. Nothing else. So how could one still mention about classical mechanics in a QFT Universe?
     
  15. Aug 10, 2016 #14
    The commonly said phrase about "four fundamental interactions" (em, weak, strong, gravity)

    https://en.wikipedia.org/wiki/Fundamental_interaction

    needs some clarification. For one, while Standard model does have strong force, there is no "fundamental EM interaction": electromagnetism is just a "fallout" of broken SU(2)*U(1). Thus, SM has three "forces", if we mean that by gauge fields: strong SU(3), weak isospin SU(2), and weak hypercharge U(1). Gravity is not explained by SM, but it clearly exists. So yes, four forces, but not ones commonly enumerated.

    And then, there are in fact more interactions in SM. Higgs "gives mass to fermions". That's interaction. Not linked to a gauge field, but still, it is an interaction.

    I would say each non-self-interacting term (i.e. a term with more than one field) in the Lagrangian is an interaction. Apart from three interaction terms for the above mentioned interactions of gauge fields with fermions, there are W*phi and B*phi terms for weak isospin and weak hypercharge fields interacting with Higgs field (since Higgs is not a fermion, these terms look different and I think this means it's a different interaction). And lastly, Yukawa interaction terms ("Higgs gives mass to fermions"), fermions*phi.

    Thus, SM has six interactions. Plus gravity, it makes seven.
     
    Last edited: Aug 10, 2016
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