Real life: Not in real life on this universe but It is possible on opposite universe.

Theory: if energy is negative but mass is positive, c^2 = (-) so speed is imaginary. Or oppositely if there is an antimatter but energy is normal, then c^2= (-) again.

Theorically possible.

No, *mathematically* possible. You have to learn the difference between what is mathematically allowed and what is physically possible.

Einstein's E = mc^2 gives an equivalence between mass at rest and its equivalent energy. You can't just put a negative sign on one side and then - because mass is always positive - conclude that Whee!! the speed of light must be imaginary. For your information the equivalent energy in that equation is always positive.

So you are just playing with mathematical symbols, but that doesn't mean there is any physics behind what you are doing. Sorry, not impressed.

You're wrong.

mass should be negative if we are talking about antimatter. research about "what is antimatter". This is theorically possible. You can say about it phsically or mathemetically possible, anyhow it is possible. If you write Einstein's law E = mc^2, there is two answers for mass. One of positive and the other one is negative. You can find out a knowledge about this matter by searching about Paul Dirac.

His research marked the first time something never before seen in nature was “predicted” – that is, postulated to exist based on theoretical rather than experimental evidence. His discovery was guided by the human imagination, and arcane mathematics.

For his achievement Dirac was awarded the Nobel prize for physics in 1933 at the age of 31.

I saw some news about some experiments antimatter found on CERN, but i don't know are they published the results or not. If it is phsically impossible, why are scientists working on it?