Neutrino Mass Bounds in the era of Tension Cosmology (2112.02993v1)

Abstract: The measurements of Cosmic Microwave Background anisotropies made by the Planck satellite provide extremely tight upper bounds on the total neutrino mass scale ($\Sigma m_{\nu}<0.26 eV$ at $95\%$ C.L.). However, as recently discussed in the literature, Planck data show anomalies that could affect this result. Here we provide new constraints on neutrino masses using the recent and complementary CMB measurements from the Atacama Cosmology Telescope DR4 and the South Polar Telescope SPT-3G experiments. We found that both the ACT-DR4 and SPT-3G data, when combined with WMAP, mildly suggest a neutrino mass with $\Sigma m_{\nu}=0.68 \pm 0.31$ eV and $\Sigma m_{\nu}=0.46_{-0.36}^{+0.14}$ eV at $68 \%$ C.L, respectively. Moreover, when CMB lensing from the Planck experiment is included, the ACT-DR4 data now indicates a neutrino mass above the two standard deviations, with $\Sigma m_{\nu}=0.60_{-0.50}^{+0.44}$ eV at $95 \%$, while WMAP+SPT-3G provides a weak upper limit of $\Sigma m_{\nu}<0.37$ eV at $68 \%$ C.L.. Interestingly, these results are consistent with the Planck CMB+Lensing constraint of $\Sigma m_{\nu} = 0.41_{-0.25}^{+0.17}$ eV at $68 \%$ C.L. when variation in the $A_{\rm lens}$ parameter are considered. We also show that these indications are still present after the inclusion of BAO or SN-Ia data in extended cosmologies that are usually considered to solve the so-called Hubble tension. A combination of ACT-DR4, WMAP, BAO and constraints on the Hubble constant from the SH0ES collaboration gives $\Sigma m_{\nu}=0.39^{+0.13}_{-0.25}$ eV at $68 \%$ C.L. in extended cosmologies. We conclude that a total neutrino mass above the $0.26$ eV limit still provides an excellent fit to several cosmological data and that future data must be considered before safely ruling it out.

• The paper derives new constraints on total neutrino mass using ACT, SPT, and WMAP data, explicitly avoiding the Planck lensing anomaly that affects its neutrino mass bounds.
• Key findings suggest that non-Planck CMB data does not exclude neutrino masses greater than 0.26 eV and can even mildly favor masses larger than the minimum expectation.
• The results are significant for tension cosmology, indicating that higher neutrino masses can correlate with higher Hubble constant values in extended cosmological models and highlighting the need for future data from cosmology and particle physics experiments.

Neutrino Mass Bounds in the Era of Tension Cosmology

The paper, "Neutrino Mass Bounds in the Era of Tension Cosmology," by Eleonora Di Valentino and Alessandro Melchiorri, addresses the complex cosmological constraints on the total neutrino mass, $\Sigma m_{\nu}$, leveraging insights from the Atacama Cosmology Telescope (ACT) DR4 and South Pole Telescope (SPT) SPT-3G datasets in conjunction with WMAP data. Notably, this paper provides analyses that are significant in the context of Tension Cosmology, where discrepancies between different cosmological observations challenge conventional cosmological models.

The authors focus on deriving new constraints independent of the Planck satellite's 2018 data, which, although having reported a stringent upper bound on the total neutrino mass, is marred by a persistent lensing anomaly—anomalously high gravitational lensing signals indicating possible systematic errors. Counteracting this issue, the authors utilize the ACT-DR4 and SPT-3G datasets, which are not affected by such lensing anomalies, making them robust candidates for revising current constraints on $\Sigma m_{\nu}$.

In their analysis, the paper presents results for both standard $\Lambda$CDM and extended cosmological models that include variations in the effective neutrino number $N_{\rm eff}$, dark energy equation of state $w$, and spectral index running $dn/dlnk$. These additional parameters are especially relevant in light of the existing Hubble constant ($H_0$) and $S_8$ tensions between early universe (CMB) and late universe (local) measurements.

Key findings demonstrate that ACT and SPT data mildly suggest a neutrino mass larger than the minimum expectation of $0.06$ eV, standing at $\Sigma m_{\nu}=0.68 \pm 0.31$ eV and $\Sigma m_{\nu}=0.46_{-0.36}^{+0.14}$ eV at $68 \%$ confidence level (C.L.) for ACT-DR4 and SPT-3G respectively, when combined with WMAP. More strikingly, when including Planck's CMB lensing data, ACT-DR4 recognizes a neutrino mass above two standard deviations: $\Sigma m_{\nu}=0.60 \pm 0.25$ eV at $68 \%$ C.L., consistent with Planck's own CMB+Lensing constraints when $A_{\rm lens}$ is varied.

The incorporation of additional datasets such as Baryon Acoustic Oscillations (BAO) and Type Ia Supernovae (SN-Ia) further refines these bounds but does not exclude $\Sigma m_{\nu} > 0.26$ eV at the $95\%$ confidence level, even within extended parameter space scenarios. Notably, the authors find that in extended cosmologies capable of addressing the Hubble tension, higher neutrino masses correlate with higher $H_0$ values, contrary to LCDM predictions that suggest lower $H_0$ for higher $\Sigma m_{\nu}$.

These results have substantial implications. Firstly, they challenge the conventional lower bounds on neutrino mass based on Planck data alone, suggesting that cosmological experiments might be on the cusp of aligning closer with laboratory measurements of neutrino mass. This requires careful consideration, especially for experiments targeting direct neutrino mass detection such as KATRIN and future $0\nu\beta\beta$ decay searches.

Additionally, embracing the notion of extended cosmological models allows researchers to explore solutions to persistent tensions in cosmological parameters, potentially unveiling new physics. Moving forward, the integration of upcoming astrophysical datasets with refined measurements in other sectors of cosmology will be crucial to conclusively determine neutrino masses and further delineate the composition of the universe.

In summation, the authors conclude that cosmological data, independent of Planck's $A_{\rm lens}$ anomaly, does not conclusively rule out neutrino masses exceeding $0.26$ eV, and emerging data may warrant revisiting current neutrino mass constraints. Future data from both cosmology and particle physics will be critical to sharpen these conclusions, deepen our understanding of neutrino properties, and elucidate potential new physics beyond the standard model.