We discuss the problem of defining a preferred vacuum state at a given time for a quantized scalar field in Friedmann, Lemaître, Robertson, Walker space-time. Among the infinitely many homogeneous, isotropic vacua available in the theory, we show that there exists at most one for which every Fourier mode makes a vanishing contribution to the adiabatically renormalized energy-momentum tensor at any given instant. For massive fields such a state exists in the most commonly used backgrounds in cosmology and, within the adiabatic regularization scheme, provides a natural candidate for the "ground state" at that instant of time. The extension to the massless and the conformally coupled case are also discussed.
|Physical Review D - Particles, Fields, Gravitation and Cosmology
|Published - Mar 23 2015
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)