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Now that the dust has settled on the 2011 superluminal neutrino debacle at OPERA, I'm interested in understanding the current status of experimental searches for neutrinos. Although the OPERA claim was a fun puzzle for theorists trying to find explanations, the claimed scenario wasn't anything like our current best guess as to what to look for in a search for tachyons. E.g., we do expect tachyons to be electrically neutral (pace Baldo 1970), but we also really expect them to have spin 0.

The only particle-physics test I've been able to locate information about is Alvager 1968. They searched for production by photons on lead and put an upper limit on the cross-section. The experiment would only have been sensitive to charged tachyons. This is extremely old, predates the modern understanding of how tachyons fit into QFT, and is of less interest than searches for neutral tachyons, which are what we actually expect to exist.

There is a big bibliography here, but it mostly focuses on the OPERA debacle.

Recami 2009 is a recent review article, but I don't have access to the conference proceedings, and the article doesn't seem to be available online.

Tachyons are expected to exist as waves that are either localized or superluminal, but not both (Shay 1977, Baez). So it seems like superluminal propagation of a wave packet, as in the OPERA result, is not really the right experimental signature to look for. What is the right signature? Non-electromagnetic Cerenkov radiation?

If they're expected to be nonlocalized, does it make more sense to look for cosmological evidence, as in Davies 2012?

It seems tough to define an appropriate way to search for tachyons, since QFT basically says they shouldn't be able to exist in the naive classical sense envisioned 50 years ago. On the other hand, the willingness of theorists to try to explain the OPERA results suggests that there is wiggle room. If you look at a freshman text like Tipler 2003, he's still referencing Alvager 1968 as the null experimental result on tachyons. This seems unsatisfactory. I can't believe that there haven't been better direct searches in the last 45 years.

This question is similar to, but much more specific than, a previous question: Tachyon and Photons

Alvager and Kreisler, "Quest for Faster-Than-Light Particles," Phys. Rev. 171 (1968) 1357, http://adsabs.harvard.edu/abs/1968PhRv..171.1357A

Baez - http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html

M.Baldo, G.Fonte & E.Recami: “About charged tachyons”, Lett. Nuovo Cim. (first series) 4 (1970) 341-247. http://dinamico2.unibg.it/recami/erasmo%20docs

P. C. W. Davies, Ian G. Moss, "Cosmological bounds on tachyonic neutrinos" http://arxiv.org/abs/1201.3284

Recami, "Superluminal waves and objects: An overview of the relevant experiments," Journal of Physics: Conference Series, Volume 196, Issue 1, article id. 012020, 14 pp. (2009)

Shay and Miller, "Causal and noncausal propagation of both tardyon and tachyon wave functions," Nuovo Cimento A 38 (1977) 490, http://link.springer.com/article/10.1007%2FBF02730018

Tipler, Modern Physics, 2003

[EDIT] I did succeed in finding some references more recent than 1968. I don't know if these represent the state of the art, but to avoid wasting other people's time, I'll list them here:

Clay, A search for tachyons in cosmic ray showers, http://adsabs.harvard.edu/full/1988AuJPh..41...93C Australian Journal of Physics (ISSN 0004-9506), vol. 41, no. 1, 1988, p. 93-99. -- cosmic rays, time of flight

Baltay, C., G. Feinberg, N. Yeh, and R. Linsker, 1970: Search for uncharged faster-than-light particles. Phys. Rev. D , 1, 759-770, doi:10.1103/PhysRevD.1.759. -- accelerator experiment

The following are not experimental papers, but do give helpful surveys of methods of searching for tachyons:

Recami, "Superluminal Waves and Objects: Theory and Experiments. A Panoramic Introduction," ebooks.iospress.nl/Download/Pdf/28897

Sudarshan, "The nature of faster-than-light particles and their interactions" http://wildcard.ph.utexas.edu/~sudarshan/pub/1969_005.pdf

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Nice question. Helpful might be more specific references concerning the underlying geometric notions: how to define/measure "velocity" (or at least: "average speed, from starting gate to finish line"), "distance" (such as "between starting gate and finish line", or whether they are "at rest" to each other" at all), "duration" ("from start, to finish"), or what constitutes a "signal relation" (let's say "from the starting gate indicating the start to the first indication of the finish line taking notice" etc.). Perhaps some writings by J.W.Schutz, or J.L.Synge, or A.A.Robb ... ? –  user12262 May 5 '13 at 18:41
This may be of little help, but the Particle Data Book folks have issued this statement: "We no longer list for limits on tachyons and centauros. See our 1994 edition for these limits." here: pdg.lbl.gov/2013/reviews/rpp2013-rev-wimps-other-searches.pdf. It may be just my impression, but it seems, that some (mostly experimental physicists) are becoming less interested in the topic. If anybody has heard about the state of funding (an extremely important detail) for tachyon experiments, I would be delighted to hear about it. –  CuriousOne Aug 11 '14 at 22:06

2 Answers 2

A good definition of a tachyon is a field with a negative mass term. In the standard model the Higgs field qualifies. The Lagrangian of the Higgs is,

$$\mathcal{L} = |D_\mu H|^2 + \mu^2 |H|^2 -\lambda |H|^4 $$

This is a scalar field with mass $i\mu$, a tachyon. To see it travels faster than light recall that the energy is $\gamma m c^2$ where $m$ is the rest mass. For the Higgs the rest mass is imaginary and the energy is a positive number so $\gamma$ is imaginary and thus $\beta >1$. What is going on here is that one has expanded around an unstable vacuum of the theory (the physical vacuum leads to spontaneous symmetry breaking).

What I wish to explain with this example is that a tachyon is a particle property that lives on a piece of paper. Assuming causality and special relativity means tachyons can not carry information. It is then straightforward to arrange for tachyons by considering the theory around a poor choice of vacuum.

Finally I acknowledge you are after something different to my opinion. Yet I think it is worth understanding the theoretical side and in particular why many consider this to be a resolved issue.

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I don't see how this really answers the question in any way. OP wants a recent experimental search for tachyons, not a theoretical treatise as to why it shouldn't exist in the first place. –  Kyle Kanos Jan 23 at 14:45
The Higgs has been discovered and may be interpreted as a tachyon. I feel that is a relevant point but I acknowledged in my answer not all would feel that way. –  Drone Scientist Jan 23 at 14:51

PROOF TACHYONS EXIST- in the old double slit experiment the DATA that determines the quantum state of the wave or particle is moved at a distance greater than light can travel and cover. The DATA of the quantum particle or wave is transferred by tachyons and cover the distance from the detector to the data faster than light showing that a tachyon has energy to effect the quantum state in the double slit experiment faster than light covers the same distance showing the effects of the tachyon and its speed. It is not entanglement or the results would of been detected a head of time.

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