The tachyon has a spin of 0, does any other particle have a spin of 0?
This I think refers to the tachyon "problem" in string theories, which is the lowest angular momentum particle along the trajectory (so is probably a scalar ).I have trouble with this. First, nobody has seen a tachyon. Second, a spin-1/2 or spin-1 tachyon is no more and no less likely than a spin-0 tachyon.
Maybe *I* am the one not thinking but I don't see that a tachyon breaks Lorentz invariance. They may give problems with causality and other stuff but I don't think they break Lorentz invariance (if they do, in what way?) For example, if they travel faster than c in one frame, that will be the case in all frames. Maybe I am missing something obvious. I have never worked much with theories with tachyons but I thougth they were always written in a Lorentz inavraint form.Ack. Yes. Stupid questions. Tachyons break Lorentz invariance anyway.