# Distinguishing between Neutrinos and time-varying Dark Energy through Cosmic Time

## TL;DR

This paper explores how time-varying dark energy models can mimic neutrino effects, causing parameter degeneracies, and discusses strategies with current and future data to distinguish between neutrino properties and dark energy evolution.

## Contribution

It demonstrates the degeneracies between neutrino parameters and dark energy evolution and evaluates how multi-probe analyses can improve parameter constraints with future experiments.

## Key findings

- Current data offers limited parameter separation.
- Future experiments will better distinguish neutrino mass.
- Degeneracies persist with current multi-probe analyses.

## Abstract

We study the correlations between parameters characterizing neutrino physics and the evolution of dark energy. Using a fluid approach, we show that time-varying dark energy models exhibit degeneracies with the cosmic neutrino background over extended periods of the cosmic history, leading to a degraded estimation of the total mass and number of species of neutrinos. We investigate how to break degeneracies and combine multiple probes across cosmic time to anchor the behaviour of the two components. We use Planck CMB data and BAO measurements from the BOSS, SDSS and 6dF surveys to present current limits on the model parameters, and then forecast the future reach from the CMB Stage-4 and DESI experiments. We show that a multi-probe analysis of current data provides only marginal improvement on the determination of the individual parameters and no reduction of the correlations. Future observations will better distinguish the neutrino mass and preserve the current sensitivity to the number of species even in case of a time-varying dark energy component.