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Abstract |
Assuming a minimal A cold dark matter (ACDM) cosmology with three massive neutrinos, the joint analysis of Planck cosmic microwave background data, DESI baryon acoustic oscillations, and distance moduli measurements of type Ia supernovae from the Pantheon + sample sets an upper bound on the total neutrino mass, Sigma m(nu)less than or similar to 0.06-0.07 eV, that lies barely above the lower limit from oscillation experiments. These constraints are mainly driven by mild differences in the inferred values of the matter density parameter across different probes that can be alleviated by introducing additional background-level degrees of freedom (e.g., by dynamical dark energy models). However, in this work, we explore an alternative possibility. Since both Omega(m) and massive neutrinos critically influence the growth of cosmic structures, we test whether the neutrino mass tension may originate from the way matter clusters, rather than from a breakdown of the ACDM expansion history. To this end, we introduce the growth index gamma, which characterizes the rate at which matter perturbations grow. Deviations from the standard ACDM value (gamma similar or equal to 0.55) can capture a broad class of models, including nonminimal dark sector physics and modified gravity. We show that allowing gamma to vary significantly relaxes the neutrino mass bounds to Sigma m(nu)less than or similar to 0.13-0.2 eV, removing any tension with terrestrial constraints without altering the inferred value of 1m. However, this comes at the cost of departing from standard growth predictions: to have Sigma m(nu)less than or similar to 0.06 eV, one needs gamma > 0.55, and we find a consistent preference for gamma > 0.55 at the level of similar to 26. This preference increases to similar to 2.5-36 when a physically motivated prior Sigma m(nu)>= 0.06 eV from oscillation experiments is imposed. |
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Address |
[Giare, William; Specogna, Enrico; Di Valentino, Eleonora] Univ Sheffield, Sch Math & Phys Sci, Hounsfield Rd, Sheffield S3 7RH, England, Email: w.giare@sheffield.ac.uk; |
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