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Cherenkov radiation in vacuum

  1. Feb 27, 2013 #1
    Hello!
    The question refers to the supposed tachyons. Many experiments have been conducted based on cosmic ray studies with the following assumption:
    " If particles with u>c exist then they should emit Cherenkov radiation in vacuum. Thus... Let's detect it!"
    How can this argument stand?
    Electrodynamics tells us that Cherenkov radiation is created when a particle travells through a medium with speed higher than the speed of light in the medium. The molecules of the medium are polarized and de-polarized resulting in the emission of photons. The u>c argument leads in coherence and the observed angular distribution of the radiation.
    But the above need a medium ! Vacuum has no molecules, so ,theoretically, how could it emit?
    Thank you
     
  2. jcsd
  3. Feb 27, 2013 #2

    mfb

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    You don't need polarization of a medium - this is just a way to slow light down.

    In vacuum, a tachyon can emit a photon and conserve both energy and momentum in that process - something not possible for other particles.
     
  4. Feb 27, 2013 #3
    Ok. But why on earth it would have the same angular distribution as the cherenkov effect?
     
  5. Feb 27, 2013 #4

    mfb

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    It is the same mechanism, I think the emitted photons would have to have some special angle relative to the flight direction.
     
  6. Feb 27, 2013 #5
    It cannot be the same mechanism, since there is no coherence!
    Have you got any documentation on the subject?
     
  7. Feb 28, 2013 #6

    mfb

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    There was some publication (or at least an arXiv preprint) discussing Cherenkov radiation for superluminal neutrinos, that might be interesting.
    There is no need to have any coherence in some material. Vacuum is fine.
     
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