MINIMAL IRREVERSIBLE QUANTUM-MECHANICS - PURE-STATE FORMALISM

It is demonstrated that, making minimal changes in ordinary quantum me chanics, a reasonable irreversible quantum mechanics can be obtained. This theory has a more general spectral decomposition, with eigenvecto rs corresponding to unstable states that vanish when t --> infinity. T hese Gamov vectors have zero norm, in such a way that the norm and the energy of the physical states remain constant. The evolution operator has no inverse, showing that we are really dealing with a time-asymme tric theory. Using the Friedrichs model, reasonable physical results a re obtained, e.g., the remnant of an unstable decaying state reappears , in the continuous spectrum of the model, with its primitive energy.