On the most constraining cosmological neutrino mass bounds

We present here up-to-date neutrino mass limits exploiting the most recent cosmological data sets. By making use of the Cosmic Microwave Background temperature fluctuation and polarization measurements, Supernovae Ia luminosity distances, Baryon Acoustic Oscillation observations and determinations of the growth rate parameter, we are able to set the most constraining bound to date, $sum m_ u<0.09$ eV at $95%$~CL. This very tight limit is obtained without the assumption of any prior on the value of the Hubble constant and highly compromises the viability of the inverted mass ordering as the underlying neutrino mass pattern in nature. The results obtained here further strengthen the case for very large multitracer spectroscopic surveys as unique laboratories for cosmological relics, such as neutrinos: that would be the case of the Dark Energy Spectroscopic Instrument (DESI) survey and of the Euclid mission.

The galaxy power spectrum take on spatial curvature and cosmic concordance

The concordance of the $Lambda$CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter $Omega_K<0$. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point of view, using measurements of the full-shape (FS) galaxy power spectrum, $P(k)$, from the Baryon Oscillation Spectroscopic Survey DR12 CMASS sample. By combining Planck data with FS measurements, we break the geometrical degeneracy and find $Omega_K=0.0023 pm 0.0028$. This constrains the Universe to be spatially flat to sub-percent precision, in excellent agreement with results obtained using BAO measurements. However, as with BAO, the overall increase in the best-fit $chi^2$ suggests a similar level of tension between Planck and $P(k)$ under the assumption of a curved Universe. While the debate on spatial curvature and the concordance between cosmological datasets remains open, our results provide new perspectives on the issue, highlighting the crucial role of FS measurements in the era of precision cosmology.

Sterile neutrino self-interactions: $H_0$ tension and short-baseline anomalies

Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples to a new light pseudoscalar degree of freedom. Consistently with previous analyses, we find that the model provides a good fit to all cosmological data and allows the high value of $H_0$ measured in the local universe to be consistent with measurements of the cosmic microwave background. However, new high $ell$ polarisation data constrain the sterile neutrino mass to be less than approximately 1 eV in this scenario. Finally, we combine the cosmological bounds on the pseudoscalar model with a Bayesian inference analysis of SBL data and conclude that only a sterile mass in narrow ranges around 1 eV remains consistent with both cosmology and SBL data.

Soundness of Dark Energy properties

Type Ia Supernovae (SNeIa) used as standardizable candles have been instrumental in the discovery of cosmic acceleration, usually attributed to some form of dark energy (DE). Recent studies have raised the issue of whether intrinsic SNeIa luminosities might evolve with redshift. While the evidence for cosmic acceleration is robust to this possible systematic, the question remains of how much the latter can affect the inferred properties of the DE component responsible for cosmic acceleration. This is the question we address in this work. We use SNeIa distance moduli measurements from the Pantheon and JLA samples. We consider models where the DE equation of state is a free parameter, either constant or time-varying, as well as models where DE and dark matter interact, and finally a model-agnostic parametrization of effects due to modified gravity (MG). When SNeIa data are combined with Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements, we find strong degeneracies between parameters governing the SNeIa systematics, the DE parameters, and the Hubble constant $H_0$. These degeneracies significantly broaden the DE parameter uncertainties, in some cases leading to ${cal O}(sigma)$ shifts in the central values. However, including low-redshift Baryon Acoustic Oscillation and Cosmic Chronometer measurements, as well as CMB lensing measurements, considerably improves the previous constraints, and the only remaining effect of the examined systematic is a $lesssim 40%$ broadening of the uncertainties on the DE parameters. The constraints we derive on the MG parameters are instead basically unaffected by the systematic in question. We therefore confirm the overall soundness of dark energy properties.

Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches

We provide a consistent framework to set limits on properties of light sterile neutrinos coupled to all three active neutrinos using a combination of the latest cosmological data and terrestrial measurements from oscillations, $beta$-decay and neutrinoless double-$beta$ decay ($0 ubetabeta$) experiments. We directly constrain the full $3+1$ active-sterile mixing matrix elements $|U_{alpha4}|^2$, with $alpha in ( e,mu ,tau )$, and the mass-squared splitting $Delta m^2_{41} equiv m_4^2-m_1^2$. We find that results for a $3+1$ case differ from previously studied $1+1$ scenarios where the sterile is only coupled to one of the neutrinos, which is largely explained by parameter space volume effects. Limits on the mass splitting and the mixing matrix elements are currently dominated by the cosmological data sets. The exact results are slightly prior dependent, but we reliably find all matrix elements to be constrained below $|U_{alpha4}|^2 lesssim 10^{-3}$. Short-baseline neutrino oscillation hints in favor of eV-scale sterile neutrinos are in serious tension with these bounds, irrespective of prior assumptions. We also translate the bounds from the cosmological analysis into constraints on the parameters probed by laboratory searches, such as $m_beta$ or $m_{beta beta}$, the effective mass parameters probed by $beta$-decay and $0 ubetabeta$ searches, respectively. When allowing for mixing with a light sterile neutrino, cosmology leads to upper bounds of $m_beta < 0.09$ eV and $m_{beta beta} < 0.07$ eV at 95% C.L, more stringent than the limits from current laboratory experiments.

Neutrino Mass Ordering at DUNE: an Extra $ u$-Bonus

We study the possibility of extracting the neutrino mass ordering at the future Deep Underground Neutrino Experiment using atmospheric neutrinos, which will be available before the muon neutrino beam starts being perational. The large statistics of the atmospheric muon neutrino and antineutrino samples at the far detector, together with the baselines of thousands of kilometers that these atmospheric (anti)neutrinos travel, provide the ideal ingredients to extract the neutrino mass ordering via matter effects in the neutrino propagation through the Earth. Crucially, muon capture by Argon provides excellent charge-tagging, allowing to disentangle the neutrino and antineutrino signature. This is a critical extra benefit of having a Liquid Argon Time Projection Chamber as far detector, that could render a $4sigma$ extraction of the mass ordering after ten years of exposure.