There was a young lady named Bright,
Whose speed was far faster than light.
She went out one day,
In a relative way,
And returned the previous night!
-Reginald Buller
It is a well known fact that nothing can travel faster than the speed of light. At best, a massless particle travels at the speed of light. But is this really true? In 1962, Bilaniuk, Deshpande, and Sudarshan, Am. J. Phys. 30, 718 (1962), said "no". A very readable paper is Bilaniuk and Sudarshan, Phys. Today 22,43 (1969). I give here a brief overview.
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"The orthodox argument against real tachyons is that they will destabilize the vacuum and cause a phase transition like the inflation creation of the universe. In a sense spontaneous breakdown of continuous symmetries, e.g. normal metal to a superconductor is a tachyonic instability of the ground state. The imaginary mass tachyon converts to a zero mass Goldstone particle and a non-zero positive real mass Higgs particle in the simplest model of a Mexican Hat Potential for a spin zero scalar field." - Jack Sarfatti
The zero mass Goldstone particles are quanta of motions round the rim and the positive mass Higgs particles are the quanta of motions up the sides the the potential energy barrier of the tachyonic scalar field with nonlinear self-coupling.