Nonlinear matter spectra in growing neutrino quintessence

TL;DR

This paper studies the nonlinear evolution of matter power spectra in growing neutrino quintessence, highlighting how neutrino inhomogeneities influence cosmic structure and oscillations, with implications for the scenario's observational viability.

Contribution

It provides the first detailed analysis of nonlinear matter spectra and acoustic oscillations in growing neutrino quintessence, emphasizing the impact of neutrino-induced gravitational potentials.

Findings

Neutrino fluctuations are linear at redshift ~5 with acoustic oscillations.

Neutrino perturbations become nonlinear around redshift ~3.

Nonlinearities erase oscillations in the neutrino spectrum above redshift 2.

Abstract

We investigate the nonlinear power spectra of density perturbations and acoustic oscillations in growing neutrino quintessence. In this scenario, the neutrino mass has a strong dependence on the quintessence field. The induced coupling stops the evolution of the field when the neutrinos become nonrelativistic, and triggers the transition to the accelerating phase of the cosmological expansion. At redshifts around five, the neutrino fluctuations are still linear and acoustic oscillations are present in the neutrino power spectrum, induced by the acoustic oscillations in the baryonic and dark-matter sectors. The neutrino perturbations become nonlinear at redshifts around three. The mode coupling generated by the nonlinearities erases the oscillations in the neutrino spectrum at some redshift above two. There is a potential danger that at later times the influence of the gravitational potentials induced by the neutrino inhomogeneities could erase the oscillations from the baryonic and dark-matter spectra, making the scenario incompatible with observations. For the scenario to be viable, the neutrino-induced gravitational potentials in the range of baryonic acoustic oscillations should not grow to average values much larger than 10^{-4}. The magnitude of the expected potentials is still not known reliably, as the process of structure formation is poorly understood in growing neutrino quintessence.