# Experimental searches for tachyons

1. ### bcrowell

5,682
Staff Emeritus
I'm working on an open-source textbook on special relativity. The text below is what I currently have on experimental searches for tachyons. There seems to have been quite a bit of work on this kind of thing in the 60's, but very little in more recent times. Does anyone know of any better empirical evidence than what I refer to below?

The most obvious experimental signature of tachyons would be propagation at speeds greater than c. Negative results were reported by Murthy and later by Clay,[9] who studied air showers generated by cosmic rays to look for precursor particles that arrived before the first photons. One could also look for particles with |p| > E. Alvager and Erman, in a 1965 experiment, studied the beta decay of 170Tm, using a spectrometer to measure momentum and a solid state detector to determine energy. An upper limit of one tachyon per 10^4 beta particles was inferred. Experimental searches are made more difficult by conflicting theoretical claims as to whether tachyons should be charged or neutral, whether they should have integral or half- integral spin, and whether the normal spin-statistics relation even applies to them.[10] Current thinking in quantum field theory is that tachyonic fields actually would not have a superluminal signal velocity, and that tachyonic fields are to be interpreted not as real physical phenomena but as unphysical features of certain field theories.[11] A brief flurry of reawakened theoretical interest in tachyons was occasioned by a 2011 debacle in which the particle-physics experiment OPERA mistakenly reported faster-than-light propagation of neutrinos; the anomaly was later found to be the result of a loose connection on a fiber-optic cable plus a miscalibrated oscillator.

[9] “A search for tachyons in cosmic ray showers,” Austr. J. Phys 41 (1988) 93, http://adsabs.harvard.edu/full/1988AuJPh..41...93C

[10] Feinberg, Feinberg, Possibility of Faster-Than-light Particles,'' Phys Rev 159 (1967) 1089, http://www.scribd.com/doc/144943457...r-Than-light-Particles-Phys-Rev-159-1967-1089

[11] Baez gives a good explanation at http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html

3. ### bcrowell

5,682
Staff Emeritus
Thanks for pointing me to that reference. I hadn't been aware of that idea.

4. ### ChrisVer

I don't really like the idea of tachyons in the general String Theory... I am sorry, but I am still a newbie in this field. But studying Strings I derived that tachyons appear only in the bosonic string theory, which of course is an unphysical theory. In the Superstrings though (where you also have fermionic degrees of freedom-thus they could be physical), the tachyon modes disappear and so they don't exist....

Also in the field point of view, the tachyons are practically unstable fields?

### Staff: Mentor

It was funny, I read your post and it just came to me to ask about magnetic monopoles. My old undergrad prof had in fact done research into detecting them early in his career in the 1930's.

Anyway, I dont recall any discussion on the connection with tachyons and so I did a search and discovered the article I posted. Serendipity I guess...

I was curious about your motivation for doing open source books. I've read some of them and they are quite good. You might be able to get Dover publications interested into mass marketing them while still keeping them as open source. I know Prof Nearing and his MathematicalTOols for Physicists book apparently has some agreement like that:

http://www.physics.miami.edu/~nearing/mathmethods/

7. ### bcrowell

5,682
Staff Emeritus
Thanks! I originally wrote books for use in my community college classes. This one is just for fun, since I don't get to teach upper-division physics.

8. ### Haelfix

1,723
The modern understanding of Tachyons is that they are NOT unphysical creatures, but rather the consequence of physicists asking the wrong questions, say asking what the positive energy excitations of a system with initial conditions right on the cusp of undergoing a phase transition are.

Whenever you see a mass term in quantum field theory that has an imaginary mass, it is always the case that it has arisen b/c the theorist in question has applied perturbation theory around an unstable point in the potential. This can be seen as a physical process in certain cases, and creates what is known as tachyon condensation where the theory quickly falls to a new ground state (with new non tachyonic stable states).

Famous examples include the Higgs field, whatever scalar field is responsible for inflation, as well as examples in condensed matter in superconductivity.

10. ### bcrowell

5,682
Staff Emeritus
Thanks, Haelfix -- that's very helpful.

I'm still curious as to whether I'm missing any good experimental literature. The experiments done in the 1960's don't seem all that hard, and it's surprising that so little has been done to improve on them.