The aim of this paper is to analyze time-asymmetric quantum mechanics with respect of its validity as a non time-reversal invariant, time-asymmetric theory as well as of its ability to determine an arrow of time.

We revise the mathematical implementation of the Dirac formulation of quantum mechanics, presenting a rigorous framework that unifies most of versions of this implementation.

The classical concept of entropy was successfully extended to quantum mechanics by the introduction of the density operator formalism. However, further extensions to quantum decaying states have been hampered by conceptual difficulties associated to the particular nature of these states. In this work we address this problem, by (i) pointing out the difficulties that appear when one tries a consistent definition for this entropy, and (ii) building up a plausible formalism for it, which is based on the use of coherent (...) complex states in the context of a path integration. (shrink)

Gamow states are vector states for the pure decaying part of a quantum resonance. We review and analyze the properties of Gamow vectors in different representations. In particular, we discuss the controversial problem of assigning a mean value of the energy for a Gamow state from several points of view. The question on whether a Gamow state is a pure state or not is also analyzed here, as has relevance on the assignation of a non-zero value for the entropy for (...) a Gamow state. (shrink)