Deriving Concepts of Tachyons: Speed, Energy & c

[greswd]

I've read somewhere that hypothetical tachyons always travel faster than c, speed up when they lose energy, and slow down when they gain energy.

And that it takes an infinite amount of energy to slow tachyons down to c.

How did they derive all these concepts?

 

[Nugatory]

I've read somewhere ... How did they derive all these concepts?

Not an easy question to answer if you won't tell us where "somewhere" is and who "they" are.
This thread is closed, but a more carefully framed question based on something that you've read in a moderately reputable source would be welcome.