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Hadrons rest mass comes from gluon field?

  1. Dec 1, 2013 #1
    I am confused on an issue relating to gluons and mass. As I understand it, quarks don't actually have a lot of rest mass. In fact, most of the rest mass found in Hadrons arises from the interactions and energy of the Gluon field between quarks(??). This sounds like GR to me, meaning that the energy of the field creates mass according to e=mc2. I am confused on a certain idea... If gluons are massless, then they have no rest-mass, like a photon. This means that they do not interact with the Higgs field. How then can the higgs field impart mass to the entire energy of the hadron, if the higgs field cannot interact with the gluons??

    I'm not sure if I'm getting the language correct. I think the center of my question revolves around the idea that the Higgs mechanism is giving mass to particles, but how does the hadron gain so much rest mass, if the Higgs only interacts with a fraction of the particles than constitute it?
  2. jcsd
  3. Dec 1, 2013 #2
    You are right.

    Higgs field gives masses to the quarks. These then form bound states with the gluons.

    So the strong force is responsible for the majority of visible mass in the universe. Not the Higgs field.

    But is your question more about binding energy?
  4. Dec 1, 2013 #3
    Hi. Ok, so I don't understand, if the Higgs is responsible for 'slowing down' particles and giving them rest mass, so that they can stand still and not move at the speed of light all the time, like a photon, I'm assuming this is where their inertia comes from. But if the Higgs imparts inertia, how can a hadron gain inertial mass from the gluon field if it doesn't interact with the Higgs. I understand that the energy of the gluon field will effect gravitational mass (e=mc2), but objects are still heavy and have inertia when I push them side ways, like a car trying to speed up or slow down. Isn't this inertia imparted entirely from the Higgs field? How does the Higgs field accomplish imparting this inertial mass to objects when most of their mass is not coming from particles that interact with the Higgs? Perhaps there a subtlety I am not seeing.
  5. Dec 1, 2013 #4
    Hi again. A thought occurred to me... I think I'm assuming that the Higgs field is directly responsible for keeping objects traveling at a constant velocity, and in fact keeping objects from achieving light speed. Perhaps this interpretation is wrong.
  6. Dec 1, 2013 #5
    Well, you might be able to argue an interpretation something like that, but I don't think it is all that helpful.

    No, according the equivalence principle inertial mass and gravitational mass are exactly the same, so the strong binding energy in hadrons results in the hadrons gaining inertial mass. Only a small part of the total mass comes from interactions with the Higgs field.
  7. Dec 2, 2013 #6


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    Hadron mass comes, primarily, from the gluon and quark sea. For nucleons, these make up about 90% of the mass, with about 9% in self-energy of the valence quarks, and only about 1% is mass of the valence quarks themselves.

    Basically, forget the old schoolbook picture of a nucleon as three quarks tied by some gluons. A nucleon is an entire soup of quarks, antiquarks, and gluons, and almost all of the mass is due to interaction and kinetic energies of these.
  8. Dec 2, 2013 #7
    The Higgs field only gives mass to the fundamental particles. Like others have said, most of the visible mass in the universe is from strong interactions within protons and neutrons. E=mc^2 is a fundamental concept of SR that is completely separate from the Higgs mechanism.

    Without the Higgs we would still have hadrons, just no atoms since electrons would not be able to bind to nucleons
  9. Dec 2, 2013 #8


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    You mean because of the mass? Electrons would still have self-energy, so they'd still be effectively massive. Or are you saying there would not be electromagnetic interaction? I don't see why that would be true, either. Could you, please, clarify?
  10. Dec 2, 2013 #9
    Well the first part of what I said is about QCD. Massless quarks would still hadronize, and protons and neutrons would look nearly the same (pions would be massless though due to the perfect SU(2) symmetry and the strong nuclear force would be long range).

    For the second part, I meant that fundamental fermions would be completely massless w/o the Higgs according to the SM. Electrons would have no rest mass, and therefore the energy required to bind an electron to an atom would diverge. So essentially the universe would be composed of massless electrons and neutrinos, hadrons, and then maybe some new kind of composite massive particle from the now massless weak force (I've never gotten a straight answer about confinement in a massless SU(2) gauge theory).
  11. Dec 2, 2013 #10
    Whether or not a theory leads to confinement depends on more than your choice of gauge. It also depends on the matter content of the theory. Any non-abelian gauge theory by itself leads to confinement, but once you add fermions to your theory confinement may disappear. It all depends on the overall sign of the renormalization beta function. For QCD, for instance, we have [itex]\beta(\alpha_s)=-\left(11-\frac{2n_f}{3}\right)\frac{\alpha_s^2}{2\pi}~, [/itex] where nf is the number of fermion families (that's 3 in the standard model). If the standard model had 17 or more families, the sign would flip leading to a non-confined QCD theory.
  12. Dec 2, 2013 #11
    So in a Higgs-less standard model, would the weak force produce confinement? Based on the beta function I've seen for it I'd say no, but I believe that was derived with massive gauge bosons
  13. Dec 2, 2013 #12
    The Standard model's SU(2) would be confined, but barely so, without the Higgs.
  14. Dec 2, 2013 #13


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    Without the Higgs field, the electroweak SU(2) X U(1) would still be spontaneously broken by the quark condensate that breaks the global chiral symmetry. Pions would become the longitudinal components of the W and Z.
  15. Dec 2, 2013 #14


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    Sorry, chiral symmetry is a symmetry of QCD. Why would a pion condensate break electroweak symmetry?
  16. Dec 2, 2013 #15
    The quark condensate ##\langle \bar \psi \psi \rangle = \langle \psi_L^\dagger \psi_R + \psi_R^\dagger \psi_L \rangle## is not invariant under chiral SU(2) gauge transformations (under which only the L components transform nontrivially) or under chiral U(1) transformations (under which the L and R components have different hypercharges). So it breaks electroweak symmetry for the same reason that the Higgs VEV does. So the pions, which are the Goldstone bosons corresponding to the fluctuations of this condensate, will get eaten by the W and Z.
  17. Dec 2, 2013 #16
    This is really facinating... So basically, the Higgs simply gives mass to the elementary particles, but this it seems to be somewhat of a technicality with most of the inertial mass arising from interaction energies between particles. I am curious, so then does the mass of the particles themselves arise from their energy content aswell, in someway? Perhaps they have internal structure that ultimately looks massless? I'm curious if there are serious theories that explain the particles rest-masses in the amounts they are measured. Thanks all.
    Last edited: Dec 2, 2013
  18. Dec 2, 2013 #17
  19. Dec 2, 2013 #18
    Well it is not quite like that, as someone said a few posts ago, the universe as we know it would not exist if the elementary particles remained massless.

    In the Standard Model, and most extensions, the rest masses are essentially just fitted to experiments (in the standard model this amounts to tuning how strongly the various particles interact with the Higgs field). Some GUT-type theories suggest ways that some of the rest masses might be related to each other. There are also "preon" theories in which some new strong force binds some more fundamental 'preon' particles into the particles we currently think of as elementary, with the binding energy related to their masses, analogously to what happens in hadrons. Maybe this is the sort of thing you mean, though they don't seem to be so popular these days. I don't know how such pictures mesh with the Higgs picture, since we definitely have a Higgs boson these days.
  20. Dec 2, 2013 #19
    Yes, I think I was wondering if maybe all mass can be seen as arising from massless particles and interactions, within the subatomic particles, a new layer so-to-speak (like preons). I'm assuming that would require a really big particle accelerator to blast apart quarks and leptons.

    If something like that were true, that quarks and leptons had internal structure that was massless, therefore ALL mass was arising from non-massive energy. What would this mean for the Higgs? Would it no longer be necessary?
    Last edited: Dec 2, 2013
  21. Dec 2, 2013 #20
    The Higgs is necessary to break electroweak symmetry. Massive gauge theories break down at high energies, so they need to acquire mass from SOME high energy effect, the Higgs being the simplest. The coupling of fermions to the Higgs is something I've never understood fully. It's almost like after seeing the success of the Higgs mechanism someone just decided to tack fermions onto the theory. AFAIK there is no fundamental problem with massive fermions
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