Relativistic Field Theory of Unstable Particles

I feel quite ashamed no t to be speaking a b o u t any indefinite metric. I a m going to confine my r emarks to the old familiar relativistic local field theory and discuss the p rob lem of creat ing a f ramework for the descript ion of uns table e lementary particles. I need n o t apologize for this. Of the sixteen k n o w n e lementary particles, only four — the p ro ton , the electron, the neu t r ino and the p h o t o n — are stable. The p rob lem which exercised us was the p rob lem of the cons t ruc t ion of a s tate vector in a rela­ tivistic field theory cor responding to an uns tab le e lementary particle.