Constraining matter-bounce scenario from scalar-induced vector perturbations

TL;DR

This paper investigates how secondary vector perturbations, generated by scalar fluctuations in matter-bounce cosmologies, can become large enough to challenge the viability of these models, emphasizing the importance of nonlinear effects.

Contribution

It demonstrates the significant impact of scalar-induced vector perturbations in single-field matter-bounce scenarios, which was previously underappreciated.

Findings

Secondary vector perturbations become unacceptably large in many scenarios.

Scalar-induced vectors can threaten the viability of matter-bounce models.

The results highlight the need to consider nonlinear effects in bouncing cosmologies.

Abstract

Bouncing cosmologies, while offering a compelling alternative to inflationary models, face challenges from the growth of vector perturbations during the contracting phase. While linear vector instabilities can be avoided with specific initial conditions or the absence of vector degrees of freedom, we demonstrate the significant role of secondary vector perturbations generated by nonlinear interactions with scalar fluctuations. Our analysis reveals that in a broad class of single-field matter-bounce scenarios, these secondary vector perturbations get unacceptably large amplitudes, provided the curvature fluctuations are consistent with cosmic microwave background observations. This finding underscores the crucial importance of scalar-induced vector perturbations in bouncing cosmology and highlights the need for further investigation into their potential impact on the viability of these models.