While hunting around for information about the recent OPERA measurement that hints at superluminal neutrinos, I discovered that this idea was actually considered back in the 1980s. Wikipedia lists as references two papers by Chodos et al. (unfortunately they're paywalled so I can't access them right now), and some more recent ones dealing with the Standard Model Extension.

I'm curious: what happened to this line of inquiry? Did it get conclusively disproven at some point, or just ignored because there was never any reason to believe that tachyons exist? Or are there still people doing legitimate research on it?

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    $\begingroup$ One problem I see with this is that lower-energy neutrinos would exceed the speed of light more greatly than the high energy ones measured by OPERA, but for low-energy neutrinos we have a more strict bound thanks to the supernova measurements if I got this right. $\endgroup$ – leftaroundabout Sep 23 '11 at 16:09
  • $\begingroup$ Yeah, I had the same thought. But then again I wonder how these papers were published in the first place, if it were that easy. $\endgroup$ – David Z Sep 23 '11 at 16:11
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    $\begingroup$ @leftaroundabout: This is the correct naive impression, but it is expanding around an unstable vacuum. A relativistic tachyonic neutrino doesn't travel faster than light, it just condenses to make a Lorentz violating vacuum. $\endgroup$ – Ron Maimon Oct 1 '11 at 16:15
  • $\begingroup$ This is a duplicate of this question: physics.stackexchange.com/questions/14968/… . I gave an answer there two days ago which I believe is up to date. $\endgroup$ – Ben Crowell Nov 8 '11 at 0:01
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    $\begingroup$ @leftaroundabout: There are two main types of models that have been proposed to explain this: (1) models in which neutrinos are tachyons and there is no Lorentz violation, and (2) models in which neutrinos are not tachyons and there is a preferred frame. You are correct that the SN1987A data contradict #1. In any case, we will probably have a result later this year from the improved experiment that will show that the original result was wrong. Ron: Please give us a reference. I don't think you know what you're talking about. $\endgroup$ – Ben Crowell Nov 8 '11 at 0:07

Yes a few people wrote papers looking a tachyonic/superlumminal in the 1990s after experiments measuring the mass squared of a neutrino from tritium decay. Tritium decays with a fixed total energy into a neutrino an electron and helium-3, by the measuring the maximum energy of the electron and subtracting, you get the minimum energy of a neutrino and thus its mass. It turned out the neutrino actually seemed to have negative squared mass, (tachyonic), but this was totally within the error bars,e.g. m_{nu}^{2}=-0.67+/- 2.53 {eV}^{2}, at the Troitsk experiment. The error bar is much bigger than the data point, so it was pretty much ignored. But a number of papers where written, and several other experiment also showed negative squared mass data points.

Neutrinos have also been looked at for tachyonic behaviour because of the chiral nature. Since there only left handed neutrino, and right handed anti-neutrino (that a known so far, experiment might find sterile revered version of the known ones). This means that when the vacuum creates a neutrino anti-neutrino pair, back to back emission so opposite momentum, that the total has a spin 1. For any non-chiral particles the spin could be zero, meaning that the vacuum would decay, if the particle could exist with negative energy. But the chiral nature of the neutrino means this can't happen, and the vacuum is safe even with tachyonic neutrinos.

The small tachyonic masses (can I say measured, that would be wrong, clearly any random measurement around zero, would find a negative number half the time), however don't match the -(120 MeV) squared needed to fit the OPERA result using tachyonic neutrino, nor can it be the result of oscillating to a much more negative massed sterile state with such a large imaginary mass, since the faster than light measurement was for all the recorded particles.

  • $\begingroup$ Tachyons can't be used to transmit signals faster than light. Tachyonic neutrinos do not travel faster than light, they just produce a Lorentz violating vacuum. You can't explain OPERA using the standard notion of tachyon. $\endgroup$ – Ron Maimon Nov 27 '11 at 7:29
  • $\begingroup$ what kind of Lorentz violating vacuum? $\endgroup$ – diffeomorphism Dec 27 '14 at 1:27

protected by Community Feb 25 '14 at 16:27

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