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I am trying to understand mass. The Standard model contains an electroweak field where mass of everything comes from the Higgs field. The Standard model also contains Quantum Chromodynamics with a different reason for mass. Isn't this contradictory, since they are both part of the standard model?

Ruslan
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user78939
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  • Who says mass is caused my gluons? Are you talking about chiral symmetry breaking making the bound states of quarks far heavier than their free versions? That has really nothing to do with the Higgs masses. – ACuriousMind Apr 27 '15 at 23:31
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    @ACuriousMind he's probably confused because of the mass of hadrons is not due to it's constituents (quarks), but rather binding energy which is usually phrased as gluons and quark-antiquark virtual pairs. – Ali Moh Apr 27 '15 at 23:41

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I am trying to understand mass. The Standard model contains an electroweak field where mass of everything comes from the Higg's field. The Standard model also contains Quantum Chromodynamics with a different reason for mass. Isn't this contradictory, since they are both part of the standard model?

Basically, the Higgs "gives mass" to the known massive particles, although the masses are not determined by the Higgs alone (but are proportional to the Higgs vacuum expectation value).

For example, the W and Z bosons become massive when the Higgs breaks electroweak symmetry, whereas the photon remains massless. The Higgs Mechanics generates mass terms for the elementary fermions, e.g., electrons, as well. However, there are other contributions to the mass of composite particles like protons and so on.

For example, the mass of the "three" quark constituents of a proton doesn't add up to the mass of a proton, but that difference in mass is a little hard to explain in simple terms because QCD is asymptotically free, which basically means that QCD is hard to understand at low energies. You can basically say the mass difference can be accounted for by interactions and the interactions are mediated by gluons.

Anyways, there's no contradiction.

hft
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  • Do you know the effective contribution of the Higgs to the mass of the universe? Something like 0.05%, was it? – CuriousOne Apr 28 '15 at 01:27
  • I have no idea... – hft Apr 28 '15 at 01:27
  • I am still looking for a reliable source for that number, too. I have heard it floating around, but I have never seen a reference to a serious paper. – CuriousOne Apr 28 '15 at 01:29
  • The Higgs field gives masses to all elementary particles in the standard model. All those masses are Higgs induced http://en.wikipedia.org/wiki/Standard_Model. All other masses come from four vector kinematics of internally complex particle formations, from protons on. – anna v Apr 28 '15 at 04:08
  • @annav: careful with the use of "all". Photons are not massive. – CuriousOne Apr 28 '15 at 04:29
  • I think she was correcting my statement that sounds like it just gives mass to the W and Z. I will edit it. – hft Apr 28 '15 at 04:37
  • Yes, it is more general than the W and Z . and @CuriousOne .Well, it is a matter of greek-enlgish. A zero mass is not a mass in my vocabulary :) – anna v Apr 28 '15 at 04:45
  • OK... just wanted to make sure that not all particles become massive. :-) What's the status about neutrino masses, anyway? Doesn't the standard model require massless neutrinos unless lepton number is non-conserved or something like that? What's the current thinking now that neutrino masses seem to be well established? – CuriousOne Apr 28 '15 at 05:10
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    @CuriousOne afaik the standard model can be tweaked successfully to accommodate neutrino masses. This allows oscillations depending on whether one is in a mass eigenvector space or in a flavor eigenvector space. I think Lubos Motl has an answer here where he clarifies that charged leptons might do the same but the probabilities are minuscule. – anna v Apr 28 '15 at 05:17
  • @annav... I know the part about the mixing matrix, I was just not sure how to deal with the source of the mass and its consequences. My theory is very rusty and needs updating. :-( – CuriousOne Apr 28 '15 at 05:19
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    @CuriousOne here is the link http://physics.stackexchange.com/questions/176221/do-electrons-oscillate-into-muons-just-like-electron-neutrinos-into-muon-neutrin/176229#176229 – anna v Apr 28 '15 at 05:21
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the bare mass of every fermion in the standard model comes from the higgs field.

the bare mass of quarks too comes as such and it is something like 4 -8 MeV for the u and d quarks as contributed by higgs mechanism.

but inside a stable hadron, lets say proton, the quarks get a constituent mass due to low energy QCD which has a very high coupling constant and it enhances the constituent quark mass to about 330 MeV. That's due to the fact that in the stable low energy ground state, there is a virtual sea of gluons and quark-antiquark pairs attached to it which gives it a high mass. the reason for only QCD contributions as such in contrast to QED contributions is due to its very high coupling constant in the low energy limit (of order of ground state energy) in contrast to to the QED coupling constant which remains low.

also there are gluon gluon interactions too in QCD which don't let the gluons get very far from each quark agglomerate and as a result contribute to the mass of the agglomerate by sticking to it. this speciality is introduced to to the SU(3) gauge group structure of QCD.

Bruce Lee
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When electroweak symmetry broken spontenously, Nambu-Goldstone bosons become massive, which refer to 3 gauge boson W,Z.

QCD is a different process. Quarks can not stay 'isolated'. They should form any bound state (which refers to hadrons) with gluonic interactions. These strong interactions give mass to hadrons additionally.

aQuestion
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