Antimatter

The nature of antimatter is examined in the context of algebraic quantum field theory. It is shown that the notion of antimatter is more general than that of antiparticles. Properly speaking, then, antimatter is not matter made up of antiparticles—rather, antiparticles are particles made up of antimatter. This paper goes on to discuss whether the notion of antimatter is itself completely general in quantum field theory. Does the matter–antimatter distinction apply to all field theoretic systems? The answer depends on which of several possible criteria we should impose on the space of physical states. – 1. Introduction; – 2. Antiparticles on the Naive Picture; – 3. The Incompleteness of the Naive Picture; – 4. Group Representation Magic; – 5. What Makes the Magic Work? : 5.1 Superselection rules; 5.2 DHR representations; 5.3 Gauge groups and the Doplicher–Roberts reconstruction; – 6. A Quite General Notion of Antimatter; – 7. Conclusions. M.-M. V.