Dark energy and neutrinos along the cosmic expansion history

TL;DR

This study uses a model-independent approach to jointly reconstruct dark energy's equation of state and neutrino masses across cosmic history, revealing mostly consistency with a cosmological constant but potential deviations with specific data sets.

Contribution

It introduces a PCHIP-based, model-independent reconstruction of both dark energy and neutrino masses, allowing for flexible evolution and cross-checking against various cosmological data.

Findings

Dark energy is consistent with a cosmological constant in most cases.

Potential deviations from $w=-1$ occur with DESI data and phantom crossing.

Reconstruction of neutrino masses shows looser constraints with phantom dark energy.

Abstract

Recent cosmological measurements are hinting that dark energy may evolve, with its equation of state, $w_\mathrm{DE}$, even showing oscillatory patterns. In this work, we employ a model-independent approach to jointly reconstruct $w_\mathrm{DE}$ and the sum of neutrino masses, $\sum m_\nu$, adopting the PCHIP method with seven fixed nodes in which we allow the two parameters to vary. We employ CMB, Baryon Acoustic Oscillations and Supernovae Ia data to constrain the values of $w_\mathrm{DE}$ and $\sum m_\nu$ at each node. We conduct three different analyses in which we reconstruct $w_\mathrm{DE}$: one with fixed $\sum m_\nu=0.06~\mathrm{eV}$; one in which we allow $\sum m_\nu$ to vary, and one in which we also reconstruct $\sum m_\nu$ using the PCHIP method. We find the dark energy equation of state to be consistent with the cosmological constant scenario, except when including DESI data and allowing for phantom crossing, where we find a $95\%$ CL deviation from $w_\mathrm{DE}=-1$ around $z\sim1.2$. For neutrino masses, we obtain looser constraints when focusing on phantom dark energy, that show further early and late relaxation when reconstructing the mass via the PCHIP method.