Stationary condition in a perturbative approach for mass varying neutrinos

TL;DR

This paper introduces a perturbative method to analyze mass varying neutrinos coupled to dark energy, providing criteria for its applicability and insights into model stability and neutrino mass evolution.

Contribution

A new perturbative approach for mass varying neutrinos in arbitrary cosmological backgrounds, with criteria for its validity and implications for model stability.

Findings

The approach generalizes the stationary condition in MaVaN models.

Positivity of the squared speed of sound is independent of the stationary condition.

The method predicts neutrino mass evolution under specific constraints.

Abstract

A perturbative approach for arbitrary choices of the equation of state of the universe is introduced in order to treat scenarios for mass varying neutrinos (MaVaN's) coupled to the dark sector. The generalized criterion for the applicability of such an approach is expressed through a constraint on the coefficient of the linear perturbation on the dark sector scalar field. This coefficient depends on the ratio between the variation of the neutrino energy and the scalar field potential. Upon certain conditions, the usual {\em stationary condition} found in the context of MaVaN models together with the perturbative contribution can be employed to predict the dynamical evolution of the neutrino mass. Our results clearly indicate that the positiveness of the squared speed of sound of the coupled fluid and the model stability are not conditioned by the {\em stationary condition}.