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Gravitron Discovery?

  1. Oct 10, 2012 #1
    I was recently looking into how the Higgs Boson was somewhat discovered

    From the article I had read it had said that a Z boson was smashed and lost it's mass creating a disturbance of mass in the area forcing the creation of the Higgs

    Therefore if a Higgs Boson was created by the thurning of mass to energy why not a graviton?
    It seems as a disturbance in the Higgs Field would also affect the Gravitational Field, and if so would gravitons be created too?
     
  2. jcsd
  3. Oct 10, 2012 #2

    Drakkith

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    Gravitons may be created, but only if they actually exist. They have not been observed so far.
     
  4. Oct 10, 2012 #3
    Gravitons cannot be detected even in principle. There is absolutely no way to shield any detector from neutrinos to distinguish a graviton signal from a neutrino one.
     
  5. Oct 11, 2012 #4

    Chronos

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    Until we have some clue about graviton mass, this is an exercise in futility, IMO.
     
  6. Oct 11, 2012 #5
    Graviton has no mass. As can be verified by direct observation of emission of low frequency gravity waves. It is improbable that the energy loss could have been so exactly the predicted value unless gravitons were exactly what they are guessed to be, and travelling at light speed.

    If any source of significant numbers of high frequency gravitons existed, they would have distinctive properties. Spin 2 - something which no other fundamental particle has, though hadron excited states might - and selection rules.

    Could a high energy gravitational wave absorption event be distinguished from all other events - not just the high probability events but all low probability/forbidden line interactions?
     
  7. Oct 11, 2012 #6

    tom.stoer

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    You are invited to calculate e.g. the electron-photon marix elements in order to compare them with electron-graviton matrix elements just to compare the strength of the interaction; it's impossible to detect single gravitons
     
  8. Oct 11, 2012 #7

    mfb

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    ??
    That looks wrong.
     
  9. Oct 11, 2012 #8

    Nabeshin

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    Indeed, the impossibility might extend beyond just our crude detection apparatus. I recall reading a paper which did a rough calculation showing that any attempt to measure individual gravitational waves led to a measurement apparatus bordering on collapsing into a black hole!

    Nevertheless, just to clarify, even though we don't have a quantum theory of gravity we DO know some things about the graviton:
    1) Massless
    2) Spin 2
    3) 2 Transverse polarizations.

    These all of course come from just classical GR, which is why we expect them to hold quite generally for any realization of the graviton.
     
  10. Oct 11, 2012 #9

    tom.stoer

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    Yes.

    No.

    There are theories of quantum gravity where gravitons are not the building blocks. The most prominent one is LQG where gravitons may emerge in a certain regime as "effectice d.o.f". I agree that SUGRA and strings have gravitons as fundamental entities, but their reasoning based on classical, linearized GR translated into a perturbative, background-dependent quantum theory is their biggest obstacle towards a satisfactory theory of quantum gravity.
     
  11. Oct 11, 2012 #10
    It's irrelevant whether the graviton is fundamental or an effective d.o.f. It still has to be there, just like hadrons are effective d.o.f in QCD, but they are very much there, with the expected properties. Technically gravitons are effective d.o.f. in string theory too.
     
  12. Oct 11, 2012 #11

    tom.stoer

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    The problem is not the fact that the gravitons should have these properties but that they are universal, fundamental entities and that all this can be derived from classical GR:

    You can't derive universal properties for gravitons from classical GR only. You can neither prove the existence nor derive the properties of water molecules by quantizing the Navier-Stokes equations.
     
  13. Oct 11, 2012 #12
    But photons are existant and have no mass
    Could a gravitron be what gluons are made of
    Could the Strong Gravitational force not be seperated and just hiding in one another?
    *Just questions*
     
  14. Oct 11, 2012 #13

    Drakkith

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    Yep.

    Gluons are fundamental particles and are not made of any other particles.

    There is no such thing as a "Strong Gravitational Force". The strong force, or color force, is what holds hadrons together, and it's "bleed-through" holds nucleons together in atomic nuclei.
     
  15. Oct 11, 2012 #14
    ok i get it now
     
  16. Oct 11, 2012 #15

    Nabeshin

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    Admittedly, my knowledge of this comes more from the stringy point of view so I may have made too broad of a statement.

    I want to get on the same page here... So in a theory like LQG or what have you, gravitons may not be fundamental entities but do they nevertheless possess the three properties I mentioned? If not, do you have references for this?
     
  17. Oct 11, 2012 #16

    king vitamin

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    Being ignorant of LQG, what do you mean by effective degrees of freedom (if there is a terse answer)? I can understand the argument that gravitons are emergent at low energy (if that's what you're implying), but under the same argument photons are not building blocks of the standard model, and I would not use this as evidence that photons don't exist.
     
  18. Oct 12, 2012 #17
    Can it be proven from pure Maxwell theory that a fully circularly polarized electromagnetic wave with energy E carries angular momentum L=E/ω?

    And does it follow from general relativity that a fully circularly polarized gravitational wave with energy E carries angular momentum L=2E/ω?
     
  19. Oct 12, 2012 #18

    tom.stoer

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    It's difficult b/c polarized plane waves are not localized and therefore not normalizable; the integrals will always diverge. But what you can do is either to construct wave packets or to look at the local densities w/o integration.

    For the electromagnetic field you have to construct the generators of the Poinare algebra which are partially related to integrals of the energy-momentum tensor. These generators correspond to expressions

    Pμ = (E,Pi), Li, Ki

    for 4-momentum, angular momentum and boost generators.

    From the local expression for the density in the integral of Li you should be able to derive that circular polarization corresponds to angular momentum.

    For gravity it's much more complicated b/c full GR does not have global Poincare invariance and therefore the above construction becomes meaningless. But what one could do is to derive similar expressions for linearized gravity, i.e. gravbitational waves propagating on a fixed Minkowski background. Then - except for the fact that the expressions are more complicated - the above mentioned construction should become possible again.
     
  20. Oct 12, 2012 #19
    Here's a dumb question: is there any evidence for GR beyond the linear terms?
     
  21. Oct 12, 2012 #20

    mfb

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    I think the linear terms are Newtonian gravity. So everything beyond that (perihelion shift, frame dragging, non-newtonian deflection of light, Shapiro delay, ...) is evidence for GR.
    The observation of accretion disks and binary pulsars allows to probe higher orders, although in an indirect way.
     
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