Dirac's formalism of quantum mechanics was always praised for its
elegance. This book introduces the student to its mathematical
foundations and demonstrates its ease of applicability to problems in
quantum physics. The book starts by describing in detail the concept of
Gel'fand triplets and how one can make use of them to make the Dirac
heuristic approach rigorous. The results are then deepened by giving the
analytic tools, such as the Hardy class function and Hilbert and Mellin
transforms, needed in applications to physical problems. Next, the RHS
model for decaying states based on the concept of Gamow vectors is
presented. Applications are given to physical theories of such phenomena
as decaying states and resonances.