Vector modes generated by primordial density fluctuations

TL;DR

This paper investigates how vector modes are generated during the radiation era from primordial density fluctuations through second-order perturbation theory, providing calculations for their power spectrum across scales.

Contribution

It introduces a detailed second-order perturbative calculation of vector mode generation from scalar density fluctuations during the radiation era.

Findings

Vector modes are generated from scalar interactions during the radiation era.

The power spectrum of generated vector modes is computed for a power-law density perturbation spectrum.

Results show the significance of these vector modes in cosmological perturbation theory.

Abstract

While vector modes are usually ignored in cosmology since they are not produced during inflation they are inevitably produced from the interaction of density fluctuations of differing wavelengths. This effect may be calculated via a second-order perturbative expansion. We investigate this effect during the radiation era. We discuss the generation mechanism by investigating two scalar modes interacting, and we calculate the power of vector modes generated by a power-law spectrum of density perturbations on all scales.