The quantum origin of cosmic structure: theory and observations

TL;DR

This paper reviews how quantum fluctuations during cosmic inflation lead to the formation of large-scale structures, discussing mechanisms like the curvaton and vector fields, and their observational signatures.

Contribution

It introduces the role of vector fields in generating curvature perturbations and explores their unique observational signatures within the inflationary paradigm.

Findings

Quantum fluctuations produce scale-invariant spectra of perturbations.

Vector fields can contribute to curvature perturbations with distinct anisotropic signatures.

Multiple mechanisms can source the observed cosmic structures.

Abstract

The particle production process is reviewed, through which cosmic inflation can produce a scale invariant superhorizon spectrum of perturbations of suitable fields starting from their quantum fluctuations. Afterwards, in the context of the inflationary paradigm, a number of mechanisms (e.g. curvaton, inhomogeneous reheating etc.) through which such perturbations can source the curvature perturbation in the Universe and explain the formation of structures such as galaxies are briefly described. Finally, the possibility that cosmic vector fields also contribute to the curvature perturbation (e.g. through the vector curvaton mechanism) is considered and its distinct observational signatures are discussed, such as correlated statistical anisotropy in the spectrum and bispectrum of the curvature perturbation.