Disentangling geometry & growth in cosmic neutrino mass constraints: a more physical split and diagnostic
Abstract
Recent cosmological data hint at a neutrino mass sum below the minimum value allowed by the neutrino mass oscillation experiments, with a preference for the opposite of massive neutrinos ("negative" neutrino masses). Since massive neutrinos impact the expansion history of the Universe, which in turn modifies the growth of structure, we ask whether such a preference originates from the observed geometry or structure growth, and whether the two agree. In this paper, we introduce a more physical split of ∑ mν into parameters ∑ mνgeo and ∑ mνgrowth based on their physical effects, with extension to negative values. We split the expansion rate at the Boltzmann-code level: ∑ mνgeo sets H(z) for distance computation, and ∑ mνgrowth sets H(z) for perturbation evolution. Combining Planck primary CMB, Planck+ACT+SPT CMB lensing and DESI BAO data, we find similar sensitivity and "negative" preference from geometry and growth with ∑ mνgeo = −0.07±0.10 eV (68% C.L.) and ∑ mνgrowth = −0.13+0.10−0.12 eV (68% C.L.). The difference of the two is a null test of the ΛCDM model, passed by current data at 0.4σ level. Forecasts on Advanced SO CMB and DESI DR3 BAO show that $0.058$ eV would be rejected at 3.0σ from the geometry channel alone, if the negative mean of ∑ mνgeo = −0.07 eV persists. The two channels can also provide a powerful new diagnostic between possible origins of the neutrino mass tension. With future CMB and BAO data, our Fisher forecasts show that an incorrect dark energy model displaces ∑ mνgeo from $0.058$ eV by $3.1−4.2σ$ and ∑ mνgrowth by $1.1−1.3σ$, while an underestimated reionization optical depth reverses the pattern, $2.7−3.6σ$ in ∑ mνgrowth against at most 0.23σ in ∑ mνgeo. (Abridged)
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BibTeX
@misc{ge2026disentangling,
title = {{Disentangling geometry & growth in cosmic neutrino mass constraints: a more physical split and diagnostic}},
author = {Fei Ge and Frank J. Qu and Hanyue Wang and Emmanuel Schaan and W. L. Kimmy Wu and Alexander Friedland},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.20977},
eprint = {2610.20977},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.20977},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - Disentangling geometry & growth in cosmic neutrino mass constraints: a more physical split and diagnostic
AU - Fei Ge
AU - Frank J. Qu
AU - Hanyue Wang
AU - Emmanuel Schaan
AU - W. L. Kimmy Wu
AU - Alexander Friedland
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.20977
UR - https://arxiv.org/abs/2610.20977
AB - Recent cosmological data hint at a neutrino mass sum below the minimum value allowed by the neutrino mass oscillation experiments, with a preference for the opposite of massive neutrinos ("negative" neutrino masses). Since massive neutrinos impact the expansion history of the Universe, which in turn modifies the growth of structure, we ask whether such a preference originates from the observed geometry or structure growth, and whether the two agree. In this paper, we introduce a more physical split of ∑ m_ν into parameters ∑ m_ν^geo and ∑ m_ν^growth based on their physical effects, with extension to negative values. We split the expansion rate at the Boltzmann-code level: ∑ m_ν^geo sets H(z) for distance computation, and ∑ m_ν^growth sets H(z) for perturbation evolution. Combining Planck primary CMB, Planck+ACT+SPT CMB lensing and DESI BAO data, we find similar sensitivity and "negative" preference from geometry and growth with ∑ m_ν^geo = −0.07±0.10 eV (68% C.L.) and ∑ m_ν^growth = −0.13^+0.10_−0.12 eV (68% C.L.). The difference of the two is a null test of the ΛCDM model, passed by current data at 0.4σ level. Forecasts on Advanced SO CMB and DESI DR3 BAO show that $0.058$ eV would be rejected at 3.0σ from the geometry channel alone, if the negative mean of ∑ m_ν^geo = −0.07 eV persists. The two channels can also provide a powerful new diagnostic between possible origins of the neutrino mass tension. With future CMB and BAO data, our Fisher forecasts show that an incorrect dark energy model displaces ∑ m_ν^geo from $0.058$ eV by $3.1−4.2σ$ and ∑ m_ν^growth by $1.1−1.3σ$, while an underestimated reionization optical depth reverses the pattern, $2.7−3.6σ$ in ∑ m_ν^growth against at most 0.23σ in ∑ m_ν^geo. (Abridged)
ER -