3 research outputs found
Feasibility of a Unitary Quantum Dynamics in the Gowdy Cosmological Model
It has been pointed out that it is impossible to obtain a unitary
implementation of the dynamics for the polarized Gowdy cosmologies in
an otherwise satisfactory, nonperturbative canonical quantization proposed for
these spacetimes. By introducing suitable techniques to deal with
deparametrized models in cosmology that possess an explicit time dependence (as
it is the case for the toroidal Gowdy model), we present in this paper a
detailed analysis about the roots of this failure of unitarity. We investigate
the impediments to a unitary implementation of the evolution by considering
modifications to the dynamics. These modifications may be regarded as
perturbations. We show in a precise manner why and where unitary
implementability fails in our system, and prove that the obstructions are
extremely sensitive to modifications in the Hamiltonian that dictates the time
evolution of the symmetry-reduced model. We are able to characterize to a
certain extent how far the model is from unitarity. Moreover, we demonstrate
that the dynamics can actually be approximated as much as one wants by means of
unitary transformations.Comment: 12 pages, version accepted for publication in Physical Review