Constraining quantum collapse inflationary models with current data: The semiclassical approach

TL;DR

This paper tests quantum collapse models of inflation against current cosmological data, finding some models slightly favored over standard cosmology when using combined CMB and BAO data, but not with CMB alone.

Contribution

It systematically analyzes collapse-based inflation models within semi-classical gravity and compares their predictions with observational data using Bayesian methods.

Findings

Some collapse models are moderately favored over $\\Lambda$CDM with combined data.

CMB data alone do not prefer collapse models over standard cosmology.

Bayesian evidence shows no preference between CSL collapse and standard models.

Abstract

The hypothesis of the self-induced collapse of the inflaton wave function was introduced as a candidate for the physical process responsible for the emergence of inhomogeneity and anisotropy at all scales. In particular, we consider different proposal for the precise form of the dynamics of the inflaton wave function: i) the GRW-type collapse schemes proposals based on spontaneous individual collapses which generate non-vanishing expectation values of various physical quantities taken as ansatz modifications of the standard inflationary scenario; ii) the proposal based on a Continuous Spontaneous Localization (CSL) type modification of the Schr\"odinger evolution of the inflaton wave function, based on a natural choice of collapse operator. We perform a systematic analysis within the semi-classical gravity approximation, of the standing of those models considering a full quasi-de sitter expansion scenario. We note that the predictions for the Cosmic Microwave Background (CMB) temperature and polarization spectrum differ slightly from those of the standard cosmological model. We also analyse these proposals with a Bayesian model comparison using recent CMB and Baryonic Acoustic Oscillations (BAO) data. Our results show a moderate preference of the joint CMB and BAO data for one of the studied collapse schemes model over the $\Lambda$CDM one, while there is no preference when only CMB data are considered. Additionally, analysis using CMB data provide the same Bayesian evidence for both the CSL and standard models, i.e. the data have not preference between the simplicity of the LCDM model and the complexity of the collapse scenario.