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6

In the context of bosonic string theory, the ground state with no oscillator excited, has a mass, $$M^2 = -\frac{1}{\alpha'}\frac{D-2}{6}$$ where $\alpha'$ is the Regge slope, satisfying $\alpha' = 1/2\pi T$, where $T$ is the tension of the spring, and $D$ are the spacetime dimensions. It seems it has an imaginary mass (providing $D\geq 3$). You may have ...


8

In addition to the Hypnosifl's answer: in lots of modern theories tachyons do not violate causality. For example, in QFT you can choose the mass-squared term in the action to have a negative sign, that would make your field's quanta tachyons. You can check it by looking at the propagator, which oscillates at space-like region and decreases exponentially ...


10

The conclusion derives from looking at how tachyon signals would behave as seen in slower-than-light inertial frames, not from trying to consider a tachyon's own "time" (if you can call it that, since a tachyon's worldline would have to be space-like, not time-like)--basically, it's a consequence of the relativity of simultaneity. It can be shown that any ...



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