Particles can move faster then photon with known frequency if we would understand that our vacuum is only a medium with known µ>1 and ε>1.

Let's see on Cerenkov's effect in gas medium. Then we shall do gas pressure lesser and do particles faster so that Cerenkov's effect would remain.  At sufficiently low pressure, we get the speed of a photon in a vacuum, but the Cherenkov effect shows that the particle velocity is greater than the speed of a photon.

So the real constant "с" is may be on some centimeters per second grater than speed of photons that we obtained in our recent experiments( before "Conference Generale des Poids et Mesures").   

This reminds me of the OPERA experiment at Grand Sasso, where some claimed to have found neutrinos faster than light, although it was finally up to a defective plug.

The neutrino detections after the explosion of supernova 1987A, 168.000 light years away are consistent with a neutrino speed near and below c. 

Trying to find something faster than light seems nowadays like trying to demonstrate PI is rational.

http://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions

http://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly

1. No, tachyons are not found yet.

2. Within the frame of  special relativity the existence of particles able to transfer information faster than light leads inevitably to the violation of causality.

3. However, within general relativity such particles do not violate causality since the modern cosmology, based on general relativity, admits the introduction of the preferred reference frame (so called comoving frame), in which the distribution of the matter in our universe is isotropic (as a consequence, the relic radiation is also isotropic in this frame). In the preferred frame the propagation of tachyons  is ordered by the retarded causality and no causal loops exist (as a consequence, no causal loops exist in any frame).

4. The introduction of the preferred frame leads to the stability of the tachyon vacuum since in this frame no negative energy tachyons exist, while the minimum of the Hamiltonian of free tachyons  (i.e. vacuum state) does exist and equals to zero.

5.  All these features can be formulated in a covariant manner, though the 2nd postulate of the special relativity, which declares the equivalence of all inertial frames, has to be replaced by a softer demand of a covariant formulation of particle theory.

6. However, neutrinos cannot be tachyons since the unitary irreducible representations of the Poincare group admit, according to E.P. Wigner, either scalar of infinite-spin faster-than-light particles only, while neutrino spin equals to 1/2 (as to the scalar tachyons, their existence is excluded by observations).

7. These and other considerations concerning faster-than-light particles are given, for example, in my note submitted to arXive:gen-ph/14073245.

Dear Sofia;

Thank you for your interesting message.

In fait, the neutrino has been and remain an elusive particle, connected to many areas of Physics: from particle physics at small scales to astrophysics and cosmology at large scales.

Concearning its possible tachyonic behaviour, I dont 

think this view is widely accepted, especially after the flavour oscillation phenomenon confirming the masses of the three

neutrinos of the SM.

The only theory containing a tachyonic particle is string theory where a spectrum of negative mass appears, and even though it is considered as unphysical.

Returning to the neutrino, I think the idea of a tachyonic neutrino has been reconsidered after the famous expriment O

PERA 2011 where a muon neutrino appeared to propapagte raster than light. But a few weeks mater, this result vas been rejected and explained as an error of mesurement.

Concearning the important article you sent me, I can not tel you about it untill I read it carefuly. It is important for me also, and thanks again.

Jours Salah.

Tachyonsare not found. 

This is also good proof that I succeeded in quantization of gravitational by reinterpretation of the Lorentz transformation according to quantum theory (Copenhagen school). Review my papers below... I explained many times SRT according to objectivity is completely wrong. 

Review my paper "Time Contraction: The Possibility of Faster Than Light without Violation of Lorentz Transformation or Causality and the Vacuum Energy Dependent" http://dx.doi.org/10.14299/ijser.2014.04.001 

http://dx.doi.org/10.14299/ijser.2014.10.002

http://dx.doi.org/10.14299/ijser.2014.04.001

It is not obvious that negative mass should be associated with faster-than-light motion. Such behavior of neutrinos is ruled out experimentally, as pointed out by Cohen and Glashow (cited in the paper by Ehrlich).

Instead, negative mass seems to indicate an instability, disallowing the existence of a stable universe with such particles. But maybe a collection of many such particle could be stable due to some mysterious, unobserved interaction effects, while still allowing a negative mass for individual neutrinos??

I am skeptical...

Tachyons have nothing to do with negative mass. Their mass squared is negative, it is right, however their momenta and energies are always real; furthermore, the energy of tachyons in the preferred reference frame is always positive, thus no instability of the universe (and anything else) can be ignited  by tachyons.     

In general, tachyons are expected to behave similarly to ordinary particles; thus being discovered they would not produce any turbulence in the physics (rather in people's minds).  This is because the template of the standard particle theory is applicable to tachyons too.                                                      

Vassili.

How to you define the energy of a particle with negative mass squared? With and without momentum?

Kinematic formulae for tachyons can be found in any popular article on the subject.

 See e.g. a paper by Gerald Feinberg in Scientific American ``Particles that go faster than light", vol.222, no.2, pp.68-73,76,77 (1970),

or by O.M.P. Bilaniuk, E.C.G. Sudarshan in Physics Today ``Particles beyond the light barrier", vol. 22, No.5, pp.43-51 (1969).

In fact, the whole story started with a paper by O.M.P. Bilaniuk, V. Desphande, E.C.G. Sudarshan in American Journal of Physics ``Meta-relativity", vol. 30, pp. 718-723 (1962), in which the concept of faster-than-light particles was introduced in the particle physics.