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Why does the higgs particle explain mass?

  1. Jun 10, 2009 #1
    An understandable explanation please.
     
  2. jcsd
  3. Jun 10, 2009 #2

    malawi_glenn

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    define "understandable"?

    One needs to know basic quantum field theory, such as "mass terms" and "gauge invariance"

    Here is the best explanation I know http://arxiv.org/pdf/0705.4264v1
     
  4. Jun 10, 2009 #3
    I meant with a few words of your own understanding. I am not going to read all this because I know it is wrong, but don't ask me how I know this, I will not tell you here.
     
  5. Jun 10, 2009 #4

    malawi_glenn

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    You have a pretty wierd attitude

    i) One can only show that the Higgs Mechanism is false by falsify the theory, eg. perform the experiment and show that it does not exists in the energy region below approx 200 GeV OR showing that there is a logical error in the reasoning behind the Higgs Mechanicsm.

    ii) WHY should I explain things since you already know it is false? Who do you think you are?

    My understanding is mathematical, the language of physics is math, and my understanding is the same as the one A. Pich presents in his lectures.

    Now I know how to make gold using sand and cofee, but don't ask me how I know it, I will not tell you here... LOL
     
  6. Jun 11, 2009 #5

    Vanadium 50

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    Which means "Please type an answer that I promise I won't bother to read".

    I agree...this is a weird attitude.
     
  7. Jun 11, 2009 #6
    You mean a brief explanation is impossible? Anyway, then a simpler question: How much is its mass supposed to be?
     
  8. Jun 11, 2009 #7

    malawi_glenn

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    Do you really think that someone will answer you given that attitude you have shown? And this answer is so easy to obtain, just use good ol google, why should we answer trivial questions?

    I can give an explanation in 3 lines depending on how much quantum field theory you know, but you are not interested - you only know that it is false but can not tell why. Why don't you try to defend your wierd attitude?
     
  9. Jun 11, 2009 #8

    malawi_glenn

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    Ok so you don't even know how Higgs generate mass, and you don't want to read about it - still you know it is false. This is really funny logic, do you apply this kind of reasoning in everything else as well?

    Why is the question regarding the Higgs mass interesting?
     
  10. Jun 11, 2009 #9
    Malawi Glenn, I would like some insight into the answer sir- if it's appropriate or possible for this thread.

    I have taken only two semesters of graduate Quantum Theory (Shankar) with some exposure to the Diraq equation. I have a novice understanding of group theory (point groups with some limited exposure to SU(N) and SO(N)). Consequently, I'm a physical/theoretical chemist and have not had the exposure or the privilege of learning the esoteric science of Quantum Field Theory. However, I have taken most of the fundamental undergraduate courses in physics such as Quantum Mechanics, Classical Mechanics, Mathematical Methods, and so forth.
     
  11. Jun 11, 2009 #10

    malawi_glenn

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    And what do you want me to do about it?

    QFT is not esoteric, it is really hands-on
     
  12. Jun 11, 2009 #11
    Just need to watch Feynman talk about it to see that. :D
     
  13. Jun 11, 2009 #12

    nicksauce

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    Yeah you shouldn't tell us here, you should go tell the Nobel committee and claim your prize.
     
  14. Jun 11, 2009 #13

    malawi_glenn

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    or rather his psychologist... :tongue:
     
  15. Jun 12, 2009 #14
    Since there's actually someone who actually want an answer, I think we should oblige. Maybe we can salvage some proper physics from this thread.

    czelaya: It is unfortunate that everyone says that the Higgs gives particles mass, because it's so simplified a statement that it's really not very true any more. In quantum field theory, several concepts of mass occurs. One is the inertia mass of an object, which is the proportion between force and acceleration. This is, however, not relativistically invariant, and changes depending on frame. Especially, it depends on the energy content of whatever it is you're measuring --- even an excited atom will be "heavier" than the same atom in the ground state --- the effect is just very small for atoms. There are two other definitions of mass of interest, both revolving around the invariant mass in special relativity. In QFT, this mass is basically just the term that sets the relation (dispersion) between momentum and energy: E^2 - p^2 c^2 = m^2 c^4. In field theory the Lagrangian will contain possibly many such terms.

    However, due to a subtle detail in QFT, it turns out that it is inconsistent to simply put such "mass terms" into the Lagrangian. It would simply violate what we observe about weak processes e.g. beta decay. Nevertheless, we observe mass for things like electrons, so there must be such a term present. The Higgs mechanism is a way to get around this problem. I'll leave explaining the details to someone else...

    Finally, I'd like to point out that this mass generation actually accounts for almost none of the mass we see in stuff like protons i.e. everything. In fact, life would be changed very little if quarks were massless. That is because the main source of mass in hadrons is due to an interplay between the strong nuclear force and Heisenberg uncertainty that creates energy --- a lot of energy --- which is actually what gives things inertial mass. In QCD the force between quarks increases linearly with separation, therefore two quarks would like to be on top of each other if at all possible. However, elementary quantum mechanics means that such strong localisation would cause great uncertainty in momentum, and thus kinetic energy. So there is a competition between wanting localisation and wanting delocalisation. This process settles on a medium, but which is still very high energy (quark masses are in the tens of MeV, baryons start at 1 GeV).

    People should stop getting so worked up about the Higgs --- it's import to theorists because without it the whole edifice gets a gaping hole. However, it is not the source of "mass" that everyone in pop-sci seems to think it is.
     
  16. Jun 12, 2009 #15

    malawi_glenn

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    Higgs field also give mass to the gauge bosons of the electroweak theory (W and Z). The gauge fields must not have a mass term in order to have a renormalizable theory. The only way to have both, is that their mass arise due to spontaneous symmetry breaking.
     
  17. Jun 12, 2009 #16
    Hes from the future.. case settled
     
  18. Jun 12, 2009 #17

    malawi_glenn

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    or maybe extraterrestrial
     
  19. Jun 14, 2009 #18

    turin

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    The weak bosons had better be pretty darn heavy ... for all our sakes, not just for the sake of HEP theorists. Masses of fundamental particles are not mere theoretical or esoteric curiosities; they have profound influence on our daily lives. Well, what I mean is that, what we are calling electromagnetism would be quite different if not for the large masses of the weak bosons. I wonder if any of our electrical devices would even work, as designed, if the electroweak force did not interact with the Higgs field. And I wonder how stable the Sun would be?
     
  20. Jun 15, 2009 #19
    Phrased that oddly.

    The conjecture that if various values were slightly different it would drastically change our experienced reality isn't very useful even as a thought experiment.

    Pondering if you could change those values, or enter a region with changed values is useful as a sci-fi device, but still not particularly valid to reality because obviously those values don't seem to change within the limits of our experiments.

    Weak Bosons being heavy says there is a lot of interaction between the bodies involved during weak processes. Like bending a stick between your hands, there is a lot of interaction between your hands through the stick, does that mean the stick is "heavy" or in a more energetic state during this process?
     
  21. Jun 15, 2009 #20

    vanesch

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    Even more :smile: ! Perceived reality will not change because of progress (or lack thereof) of our understanding. It is as if one were claiming that those Higgs physicists are dangerous people, because if they make a small error, or if they are terribly wrong, suddenly our electrical equipment won't work anymore as it did before :bugeye:

    genneth gave, I suppose, the shortest possible "handwaving" answer to the OP question, which I will reformulate here:

    In a "normal" quantum field theory, the mass of a particle associated to a field phi is given by a term 1/2 m^2 phi^2 in the Lagrangian.

    So if you have a complicated field theory, containing a field f, and you want to know if with that field, there corresponds a particle with a certain mass, you have to look for the f^2 term in the lagrangian. If you find a term a f^2, then this means that the mass of that particle will be sqrt(2 a).

    This was simple. Turns out that the special kind of quantum field theory people are fond of for different reasons, are theories which have what one calls gauge invariance. Unfortunately, gauge invariance doesn't allow a term of the form 1/2 m^2 phi^2.

    So people devised another way to get a term that *looks like* a term 1/2 m^2 phi^2 at low energies, and hence looks like as if particles have inertial mass. And the Higgs does that.
     
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