> Without breaking free of relativity completely I have wondered
> if an object could possess negative mass? If so could it
> exceed 186,000 mps?
Hasn't the negative mass thing been debunked? Mass by definition is always positive. Tachyons were invented as a catch-all explanation for solutions to special relativity problems that had speeds greater than that of light.
In theory, a negative mass particle would be kind of weird and violate all kinds of energy conditions--for example, it would be repelled by gravity instead of attracted to it. In order to not violate Newton's 2nd law, all three forms of mass--inertial, active gravitational, and passive gravitational--have to be negative as well. Then you have to take into account the conservation of momentum.
In theory, of course.