Tachyonic Energies in a Minkowski Metric

[gravitowell]

So I'm working on a problem (Hartle problem 6, chapter 6) dealing with tachyons. So far, I have determined the four-velocity and the four-momentum (up to a sign) of a tachyon. I have, with the four-velocity being a unit spacelike four-vector,
$u^{\alpha}=\frac{\pm 1}{\sqrt{\vec{V}^2-1}}(1,\vec{V})$

(Sorry about the bad formatting...).

I don't want to just assume the positive values of $u^{\alpha}$.

I need help figuring out how to find the energy E given that p=mu.

I realize I may have not phrased my dilemma well, so please ask for clarification.

 

[elfmotat]

I couldn't find this problem in Hartle. Problem 6 in chapter 6 is about transforming into the coordinates of an accelerated frame. I'm also not really sure what your question is.

 

[Nabeshin]

Don't really have time to comment on the OP's dilemma, but I believe it's ch.5 problem 23.

 

[gravitowell]

Yes, you're right. I was about to change it. Thanks for noting.

 

[gravitowell]

I figured it out. I found my energy-momentum for tachyons to be given by

E^2=p^2-m^2.