[@Ozerath]

As far as anti-gravitons go. Scientists do not even know if gravitons exist in the first place and anti-gravitons wouldn't work, as far as our scientists believe. Mainly because we don't have a quantum theory on gravity just yet. 

As far as positrons as weapons go, they would literally annihilate any matter that it comes into contact with. In space it could work, but it would be hard and could destroy the weapon. As missile it could work, but it would be impractical because of the energy it would require to keep the positrons in place.