Violation and Restoration of Probability Positivity in Perturbative Quantum Field Theory: From Quantum Mechanics to Quantum Chromodynamics
In quantum mechanics the modulus square of the wave function is the probability of an event --- positivity is self-evident. Quantum field theory corresponds to quantum mechanics one-to-one: the wave function corresponds to the matrix element, so the probability of a process should be the modulus square of the matrix el...