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When One-Parameter Dark Energy Makes Neutrinos Physical Again

Weiqiang Yang, Eleonora Di Valentino, Eric V. Linder, Sibo Zhang, Supriya Pan

Abstract

A puzzling implication of current data interpreted in the $Λ$CDM cosmology is the preference for a negative sum of neutrino masses. Moving to $w_0w_a$CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case $w$CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing $w=-1$ at lower redshift.

When One-Parameter Dark Energy Makes Neutrinos Physical Again

Abstract

A puzzling implication of current data interpreted in the CDM cosmology is the preference for a negative sum of neutrino masses. Moving to CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing at lower redshift.
Paper Structure (10 sections, 10 equations, 4 figures, 7 tables)

This paper contains 10 sections, 10 equations, 4 figures, 7 tables.

Table of Contents

  1. Introduction
  2. One parameter Dynamical Dark Energy
  3. Observational data and methodology
  4. Results
  5. Physical Interpretation
  6. Thawing
  7. Generalized Thawers
  8. Mirage
  9. GEDE
  10. Summary and Conclusions

Figures (4)

  • Figure 1: Evolution of $w(z)$ for the generalized thawing dark energy models, for three values of $p$. In this figure we fix $w_0=-0.8$ to focus on the steepness of the evolution for the different cases of $p$. The horizontal dotted line shows $w=-1$.
  • Figure 2: 68% and 95% CL constraints on $\sum m_{\nu,{\rm eff}}$ and $w_0$ for each class of one-parameter dynamical DE models, for the combined dataset CMB+DESI+SN Ia where one of the four compilations of the SN Ia dataset is considered at a time. Top row$-$thawing, mirage, GEDE; Bottom row$-$generalized thawers with $p=1$, $5$, $15$ (from left to right).
  • Figure 3: 68% and 95% CL constraints on $\sum m_{\nu,{\rm eff}}$ and $w_0$ for each of the one-parameter dynamical DE models considering the combined dataset CMB+DESI+DES-Dovekie.
  • Figure 4: 68% and 95% CL constraints on $\sum m_{\nu,{\rm eff}}$ and $\delta$ for the GEDE model considering the combined dataset CMB+DESI+DES-Dovekie, and CMB+DESI.