No, tachions are not inconsistent with relativity, but wholly consistent with it. What would be inconsistent would be if tachions could ever interact with ordinary matter, and if they do not interact with ordinary matter, then for all practical purposes tachions cannot exist within our universe.

The problem is not that relativity precludes matter travelling faster than light, but rather that matter travelling faster than light must have imaginary mass (imaginary in the sense of the square root of -1, not in the sense of being of the human imagination). Since matter travelling slower than the speed of light does not have imaginary mass, so the domains in which these imaginary mass particles and real mass particles exist must be different.

Whether at some future time someone might formulate a way in which tachions can interact with real matter, without reducing their speed to less than light speed, and where ordinary matter does not exceed light speed, is something I do not know.

The existence of tachions does not contradict E=MC^2, but since M is imaginary, it should also make E imaginary. It also has other strange properties; such as in the real world, the faster you go, the more kinetic energy you have, in the the tachion world, you have less kinetic energy as you travel faster. This is consistent, since in both worlds, to travel at the speed of light requires infinite energy, so as a tachion slows down towards the speed of light, if needs ever more energy, just as ordinary matter as it speed up towards the speed of light it requires ever more energy.

**G***eorge*