Talk by Dr. Mercedes Martin Benito

Speaker: Dr. Mercedes Matín-Benito, Radboud University, 

Title: Uniqueness of the Fock representation of Dirac fields in closed FRW cosmology.

Time: 11:00 Wednesday Nov 18 2015
Place: 241 Nicholson

Abstract:

I will discuss about the ambiguity that exists in the Fock quantization of free fields in curved spacetimes, and how to employ physically motivated criteria to fix such ambiguity and thus select a privileged Fock representation. In the familiar case of Fock quantization of free fields in Minkowski, demanding Poincaré invariance fixes the vacuum and therefore the Fock representation. In contrast, in non-stationary situations we cannot longer demand time-translation invariance to select the vacuum of the representation. We can still ask for invariance under the group of spatial isometries of the background, but in general this criterion is not enough to remove the ambiguity in the representation. Then a natural question arises: can we demand extra criteria to select a privileged vacuum? In turns out that in certain non-stationary spacetimes, such as compact cosmological spacetimes, the answer is in the affirmative: Demanding a unitary implementation of the dynamics in the quantum theory serves to select a unique (up to unitary equivalence) Fock representation. I will illustrate this fact in the particular case of a Dirac field propagating in a homogeneous and isotropic spacetime with the spatial sections given by three-spheres.