Negative neutrino masses as a mirage of dark energy (2407.10965v2)

Abstract: The latest cosmological constraints on the sum of the neutrino masses depend on prior physical assumptions about the mass spectrum. To test the accordance of cosmological and laboratory constraints in the absence of such priors, we introduce an effective neutrino mass parameter that extends consistently to negative values. For the $\Lambda$CDM model, we analyze data from Planck, ACT, and DESI and find a $2.8-3.3\sigma$ tension with the constraints from oscillation experiments. Motivated by recent hints of evolving dark energy, we analyze the $w_0w_a$ and mirage dark energy models, showing that they favour larger masses consistent with laboratory data, respectively $\sum m_{\nu,\mathrm{eff}} = 0.06_{-0.10}^{+0.15}\,\mathrm{eV}$ and $\sum m_{\nu,\mathrm{eff}} = 0.04_{-0.11}^{+0.15}\,\mathrm{eV}$ (both at 68%).

• The paper introduces an effective negative neutrino mass parameter to address tensions between cosmological data and lab measurements.
• The study uses Gaussian extensions and alternative dark energy models, finding a 2.8–3.3σ deviation in the standard ΛCDM framework.
• These results suggest that integrating evolving dark energy with neutrino physics can resolve discrepancies and guide future cosmological research.

Analyzing Negative Neutrino Masses as a Mirage of Dark Energy

The paper "Negative neutrino masses as a mirage of dark energy" presents a detailed exploration of cosmological constraints on the sum of neutrino masses and their compatibility with laboratory measurements. The primary inquiry addresses whether perceived tensions between cosmological models and lab-based neutrino mass constraints could suggest alternative dark energy phenomena. The authors challenge standard cosmological assumptions by extending the domain of neutrino masses to negative values, providing a novel perspective on cosmic observations.

Background and Motivation

Cosmological observations, particularly from the CMB and large-scale structure surveys, have been instrumental in setting constraints on the sum of neutrino masses. This paper utilizes data from Planck, ACT and DESI, and corroborates these with results from laboratory experiments such as KATRIN and KamLAND-Zen. A conventional approach within the field is to impose a lower bound based on neutrino oscillation data, yet recent results indicate that assuming a standard $\Lambda$CDM model leads to tensions with lower mass limits provided by oscillation experiments. This discrepancy incentivizes exploring beyond the vanilla cosmological models and considering modifications such as alternative dark energy forms.

Recent hints from DESI suggest that the equation of state for dark energy may evolve over cosmic time, thereby influencing the derived cosmological constraints on neutrino mass. The paper leverages this by using the $w_0w_a$ and mirage dark energy models to alleviate the neutrino mass tension, proposing that the tension itself might be a mirage or artifact of dark energy dynamics mischaracterization.

Methodology and Results

The paper introduces an effective neutrino mass parameter extending to negative values, a move aimed at disentangling systematic biases introduced by prior assumptions. A Gaussian extension of the posterior distribution is employed to handle negative mass values, accounting for the effects of neutrinos on cosmological processes without default assumptions about mass sign. The approach revealed a tension in the $\Lambda$CDM model amounting to a $2.8-3.3\sigma$ deviation with respect to oscillation-based constraints.

When alternative dark energy models are considered, particularly $w_0w_a$CDM and mirage models, the effectiveness of relieving this tension becomes evident. These models suggested effective neutrino masses of $\sum m_{\nu,\text{eff}} \approx 0.06\,\si{\eV}$ and $0.04\,\si{\eV}$ respectively, more aligned with laboratory measurements when compared to a rigid $\Lambda$CDM framework.

The analysis also emphasizes the degeneracy between the sum of neutrino masses and the dark energy equation of state, with implications that these parameters are not independently constrained and can mislead interpretations that neglect their interdependence. It's this blend of new modeling approaches and data that gives new insights into the nature of dark energy and its interplay with neutrino physics.

Implications and Future Directions

The considerations put forth in this paper deepen our understanding of cosmological models in the presence of evolving dark energy and neutrino mass constraints. A major implication is that a negative effective neutrino mass parameter might be a useful phenomenological tool in cosmology, indicating a potential shift in how upcoming observations, especially from DESI and other cosmological surveys, could be interpreted.

Moreover, this work opens avenues for more nuanced models where neutrinos and dark energy are considered in a synergistic framework, rather than in isolation. Long-term benefits could include more precise future measurements from KATRIN or potential observations of neutrinoless double-beta decay, which might further challenge the current paradigm or underpin new physics in cosmology.

Overall, the paper posits that the constraints on neutrino mass in cosmological studies must be made with an open mindset on the dark energy hypothesis, allowing for results that could vastly inform theories on cosmic evolution and particle physics. Future advancements in observational data, coupled with theoretical innovations in constraining cosmic models, stand to refine these interpretations further.