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How many higgs particles are there in the universe

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  1. Nov 10, 2013 #1

    ftr

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    And does not their mass add to the mass (or energy) of the universe? Does that not create problems in cosmological models ?

    I know about the Dark energy/higgs conjecture, but that is NOT my question.
     
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  3. Nov 11, 2013 #2

    fzero

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    The lifetime of the Higgs is probably somewhere in the range of a nanosecond, so practically all of the Higgs particles that were around at early times have decayed long ago. The small number of Higgs particles being created in particle accelerators and natural high-energy events is miniscule on cosmological scales.

    Since ##m_e/m_p < 10^{-3}##, the assumption that all of the mass density of ordinary matter is contained in nonrelativistic baryons is a very good approximation, well within present error bounds.
     
  4. Nov 11, 2013 #3

    ftr

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    So what does give present day electrons their mass then if the higgs have vanished long time ago? I thought they permeate all space now not then.

    Since I am not an expert on the subject I would really appreciate a bit more elaborate answer. And I do hope you understood my question.
     
  5. Nov 11, 2013 #4

    jtbell

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    The Higgs field, not Higgs particles, "gives" other particles their masses.
     
  6. Nov 11, 2013 #5

    ftr

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    So, do these fields carry energy or not, and how much. I have never heard of field that did not represent a particle. we never detect fields, we usually infer their existence (which even some people deny that they exist physically). we only detect particles. Of course, there is a controversy as to the nature of vector potentials representing the electromagnetic fields(photons).
     
  7. Nov 11, 2013 #6

    Drakkith

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    Who said the field didn't represent the particle?
     
  8. Nov 11, 2013 #7

    HallsofIvy

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    You seem to be misunderstanding fzero's "The lifetime of the Higgs is probably somewhere in the range of a nanosecond, so practically all of the Higgs particles that were around at early times have decayed long ago." It is NOT that the Higgs particles "existed long ago, gave fundamental particles their mass, then all decayed". The Higgs particles, like all fundamental particles, are being created and annihilated all the time. The Higgs particles that exist at any one time create the "Higgs field" that gives fundamental particles their mass but it is impossible to say that some specific number of Higgs particles exist.

     
  9. Nov 11, 2013 #8

    ftr

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    fzero said that no higgs particles exist today while jtbell said that their field exists. That is confusing, don't you think?

    But anyway, I see your profile says you are studying astronomy, so does higgs "field" pause problems for cosmological models(incase they add energy to the universe) or not.
     
    Last edited: Nov 11, 2013
  10. Nov 11, 2013 #9

    jtbell

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    The way I understand it, particles are excitations of (more visually, "ripples in") their corresponding fields. The field is "more fundamental" in some sense, and always exists, whereas particles come and go.
     
  11. Nov 11, 2013 #10

    ftr

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    It is not clear to me what you mean. first, fzero's sentence is very direct, it asserts/implies that no roaming higgs particles is to be found today. Second, AFAIK the electron is not considered popping in and out. This virtual popping in and out is a mathematical description for certain processes and not physical.

    But anyway, whether particle or field they carry energy and that creates a problem in cosmology, that is my main question. I will leave the question of Higgs particle existence to another thread.
     
  12. Nov 11, 2013 #11

    Drakkith

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    Not really. Mediating particles do not need to physically exist nearby for other particles to interact via the field. For example, if I have a hydrogen atom isolated in a box the electron and proton still interact via the EM force even though no photons are nearby.

    I don't know, I'm a freshman who has yet to take any astronomy related courses.
     
  13. Nov 11, 2013 #12
    Can Higgs particles be generated naturally by high energy objects such as quasars? I'd like to think so. :tongue:
     
  14. Nov 11, 2013 #13
    When we combine quantum mechanics and special relativity, we end up with quantum field theory. Essentially what we learn is that the field and the particle are part of the same thing. Whenever we detect a particle, what we are really detecting is that the field has been excited in that local area.

    So what this means is that even though the higgs particles are decaying quite quickly, all that means is that the field is returning to it's ground state. It's the higg's ground state that gives particles their mass, and it's always there. However, since it's not excited anywhere, we don't see any higg's particles.
     
  15. Nov 11, 2013 #14

    ftr

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    I am fairly familiar with QFT.My understanding is that particles decay to other entities and the original entity ceases to exist, also a particles and its field exist at the same time (fields are description of particles , ground state or not). That is not in the sense of electrons in higher energy state "decaying" into ground state.

    I repeat, I am only interested in understanding my original question regarding cosmology. leaving other questions for later threads.
     
  16. Nov 11, 2013 #15

    fzero

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    Ultra-high energy cosmic rays have been detected, such that a collision with an Earth proton would take place at a center of mass energy around 50 times that available at the LHC. Such a collision on Earth or elsewhere in the universe could certainly create Higgs particles. However, the number that would be produced by such processes would be far too small to have any detectable influence on cosmology.

    To OP: as others have tried to explain, there is a subtle difference between a quantum field and its quantum excitations. The field contains information about both classical and quantum physics. Sometimes this is phrased in a background field language. That is, we can decompose a field operator, ##\hat{\Phi} = \Phi_0 + \hat{\phi}## into a classical part ##\Phi_0##, which is c-number-valued, and a quantum part ##\hat{\phi}## that creates and destroys particles. The classical background value ##\Phi_0## satisfies the classical equations of motion and an allowed background corresponds to the ground state of the quantum system.

    If you recall the discussion of the Higgs effect in QFT, this split is used when discussing symmetry-breaking potentials. The Higgs potential has a local maximum at the origin where ##H_0=0## and the electroweak symmetry is unbroken. However the true minimum of the Higgs potential has ##H_0\neq 0## and the electroweak gauge symmetry is spontaneously broken by that vacuum state. This specifies the ground state, but if we introduce enough energy into our system, we can produce excited states. These are the states that contain non-zero numbers of Higgs particles.

    There is a useful real-world analogy. Consider a bar magnet. This corresponds to a nonzero background value of the magnetic field. But in a frame where we are stationary (more generally any inertial frame) with respect to the magnet, we will measure no photons. If we start shaking the magnet, we are putting energy into the system and we can start to produce photons. If we produce enough of them, we will be able to measure them as the EM radiation of an accelerating magnet.

    So we can have a ground state with no Higgs particles and some background value of the Higgs field, but we can also have excited states with some Higgs particles and the background. Most of the time, a measurement of the state of the universe would reveal that we are in the first state, with no Higgs particles. A small amount of the time, we might measure a Higgs particle, but this would happen too infrequently to affect the expansion of the universe in any meaningful way.
     
  17. Nov 11, 2013 #16

    ftr

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    Thank you for the elaborated explanation.

    I will come back to particle issue later. But I want to understand my original issue. This is a quote from wiki, and there are similar ones elsewhere.

    http://en.wikipedia.org/wiki/Higgs_boson

    "The relationship (if any) between the Higgs field and the presently observed vacuum energy density of the universe has also come under scientific study. As observed, the present vacuum energy density is extremely close to zero, but the energy density expected from the Higgs field, supersymmetry, and other current theories are typically many orders of magnitude larger. It is unclear how these should be reconciled. This cosmological constant problem remains a further major unanswered problem in physics."

    Is that an accurate assessment.
     
  18. Nov 11, 2013 #17

    fzero

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    Yes, that's accurate. The source term for the Einstein equations is the stress-energy tensor for whatever matter exists in the universe. We might expect on general grounds that any vacuum energy contributes to this. However, if we compute the vacuum energy of the Higgs field and then put it into the stress tensor, we find an effective cosmological term that is something like 45 orders of magnitude larger than the observed value. There's no accepted explanation of the observed value of the cosmological term.
     
  19. Nov 12, 2013 #18

    ftr

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    Finally found this paper if anybody is interested.

    The Higgs Mechanism and The Vacuum Energy Density Problem


    http://arxiv.org/pdf/hep-ph/0408311v2.pdf
     
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