The Model Dependence Of Cosmological Neutrino Mass Estimates

Even with greatly relaxed cosmology based bounds in neutrino mass that free it from the strong model dependence it has in the deeply flawed ΛCDM model, cosmology based limits on neutrino mass have a 90% confidence level upper bound that is about five times more strict than direct measurements of neutrino mass.

The relaxed less model dependent bound on neutrino mass still limits the lightest neutrino mass to about 60 meV in an inverted hierarchy scenario, and to about 73 meV in a normal neutrino mass hierarchy. In the restrictive and model dependent ΛCDM model estimation of the neutrino masses, there is a normal neutrino mass hierarchy and the lightest neutrino mass can't be much more than 2 meV which a best fit value that is much smaller than that.

Very low neutrino masses greatly limits the role that neutrinos can play to make up the gap between modified gravity theories that account for most, but not all, dark matter phenomena, such as MOND.

Neutrino oscillations establish that neutrinos are massive, providing the only laboratory detection of physics beyond the Standard Model. Direct kinematic experiments bound the electron-neutrino mass to m(νe) < 0.45 eV (KATRIN, 90% CL), implying ∑m(ν) ≲ 1.3 eV. 

Conversely, cosmology within ΛCDM is highly constraining: Planck CMB, CMB lensing, and DESI DR2 BAO yield ∑m(ν) < 0.056 eV (95% CL), in 2-3σ tension with the inverted-ordering floor (0.10 eV). However, this bound relies on ΛCDM, while data hint at an evolving dark energy. 

To determine the model dependence of cosmic neutrino mass bounds, we deconstruct each probe's sensitivity to late-time physics and pursue two robust routes to a ∑m(ν) bound: 

(i) The existing dark-energy-marginalized route, retaining all data and marginalizing over (w(0),w(a)), is shown to also be immune to flexible binned and cubic w(a) histories, yielding ∑m(ν) < 0.152 eV, sharpening to σ(∑m(ν)) ≈ 0.043 eV with Simons Observatory lensing and Spec-S5 BAO.

(ii) A new late-Universe-free route combines primary CMB, marginalizing over acoustic-peak smoothing via Alens, with the reconstructed lensing spectrum CκκL, removing late-time expansion dependence by construction. This yields ∑m(ν) < 0.41 eV today, tightening to 0.31 eV (Simons Observatory) and 0.28 eV (cosmic-variance limit) across all tested dark-energy models. These relaxed bounds trade statistical power for model independence. Interestingly, they land in the sensitivity range targeted by next-generation laboratory experiments like Project 8 (m(νe) ∼ 0.1 eV), motivating vital synergies between future cosmological and terrestrial neutrino measurements.

Frank J. Qu, et al., "Measuring Cosmic Neutrino Masses Independently of Dark Energy" arXiv:2607.24742 (July 27, 2026).