Kavli Affiliate: Blake Sherwin
| Summary:
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 $m_ν_e < 0.45$ eV (KATRIN, 90% CL), implying $sum m_νlesssim 1.3$ eV. Conversely, cosmology within $Λ$CDM is highly constraining: Planck CMB, CMB lensing, and DESI DR2 BAO yield $sum m_ν< 0.056$ eV (95% CL), in 2-3$σ$ tension with the inverted-ordering floor (0.10 eV). However, this bound relies on $Λ$CDM, 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 $sum m_ν$ 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 $sum m_ν< 0.152$ eV, sharpening to $σ(sum m_ν) approx 0.043$ 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 $A_rm lens$, with the reconstructed lensing spectrum $C_L^κκ$, removing late-time expansion dependence by construction. This yields $sum m_ν< 0.41$ 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 ($m_ν_e sim 0.1$ eV), motivating vital synergies between future cosmological and terrestrial neutrino measurements.
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