Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum Mechanics of Klein-Gordon-Type Fields and Quantum Cosmology   We formulate the quantum mechanics of the solutions of a Klein-Gordon-type
field equation: (\partial_t^2+D)\psi(t)=0, where D is a positive-definite
operator acting in a Hilbert space \tilde H. We determine all the
positive-definite inner products on the space H of the solutions of such an
equation and establish their physical equivalence. We use a simple realization
of the unique Hilbert space structure on H to construct the observables of the
theory explicitly. In general, there are infinitely many choices for the
Hamiltonian each leading to a different notion of time-evolution in H. Among
these is a particular choice that generates t-translations in H and identifies
t with time whenever D is t-independent. For a t-dependent D, we show that
t-translations never correspond to unitary evolutions in H, and t cannot be
identified with time. We apply these ideas to develop a formulation of quantum
cosmology based on the Wheeler-DeWitt equation for a Friedman-Robertson-Walker
model coupled to a real scalar field. We solve the Hilbert space problem,
construct the observables, introduce a new set of the wave functions of the
universe, reformulate the quantum theory in terms of the latter, reduce the
problem of time to the determination of a Hamiltonian operator acting in
L^2(\R)\oplus L^2(\R), show that the factor-ordering problem is irrelevant for
the kinematics of the quantum theory, and propose a formulation of the
dynamics. Our method allows for a genuine probabilistic interpretation and a
unitary Schreodinger time-evolution.

9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph