Vector Curvaton with varying Kinetic Function

TL;DR

This paper introduces a vector curvaton model with a varying kinetic function and mass during inflation, capable of generating scale-invariant, anisotropic, or isotropic curvature perturbations, with realistic supergravity or superstring implementations.

Contribution

It presents a novel vector curvaton model with dynamic kinetic and mass functions, enabling diverse curvature perturbation scenarios and realistic theoretical foundations.

Findings

Scale-invariant superhorizon perturbations achieved.

Potential for significant statistical anisotropy in the spectrum.

Realistic supergravity or superstring models for parameter variation.

Abstract

A new model realisation of the vector curvaton paradigm is presented and analysed. The model consists of a single massive Abelian vector field, with a Maxwell type kinetic term. By assuming that the kinetic function and the mass of the vector field are appropriately varying during inflation, it is shown that a scale invariant spectrum of superhorizon perturbations can be generated. These perturbations can contribute to the curvature perturbation of the Universe. If the vector field remains light at the end of inflation it is found that it can generate substantial statistical anisotropy in the spectrum and bispectrum of the curvature perturbation. In this case the non-Gaussianity in the curvature perturbation is predominantly anisotropic, which will be a testable prediction in the near future. If, on the other hand, the vector field is heavy at the end of inflation then it is demonstrated that particle production is approximately isotropic and the vector field alone can give rise to the curvature perturbation, without directly involving any fundamental scalar field. The parameter space for both possibilities is shown to be substantial. Finally, toy-models are presented which show that the desired variation of the mass and kinetic function of the vector field can be realistically obtained, without unnatural tunings, in the context of supergravity or superstrings.