Generalised Gaussian states in group field theory and $\mathfrak{su(1,1)}$ quantum cosmology

TL;DR

This paper introduces generalized Gaussian states within $rak{su(1,1)}$ quantum cosmology and group field theory, analyzing their semiclassical properties and criteria for cosmological relevance.

Contribution

It defines new generalized Gaussian states for $rak{su(1,1)}$ models, compares semiclassicality criteria, and discusses their construction in algebraic group field theory quantization.

Findings

Small relative fluctuations depend mainly on state displacement.

Generalized Gaussian states can be constructed in group field theory.

Semiclassicality criteria vary between fluctuation size and uncertainty saturation.

Abstract

We define generalised Gaussian states for quantum cosmological models based on the $\mathfrak{su(1,1)}$ algebra, with particular emphasis on its realisation in group field theory for a single field mode, and study their semiclassical properties. These states are generalisations of coherent, squeezed and thermal states considered previously. As two possible characterisations of semiclassicality, we contrast the requirement of small relative fluctuations in volume and energy with the saturation of the Robertson--Schr\"odinger uncertainty principle. We find that for the most general class of states the appearance of small relative fluctuations, which we take as the main criterion relevant for the emergence of cosmology, is mostly determined by the amount of displacement used to define the state. We also observe that defining such generalised Gaussian states is less straightforward in the algebraic approach to canonical quantisation of group field theory, and discuss special cases.