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Hagstotz, S., de Salas, P. F., Gariazzo, S., Pastor, S., Gerbino, M., Lattanzi, M., et al. (2021). Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches. Phys. Rev. D, 104(12), 123524–20pp.
Abstract: We present 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 nu beta beta) experiments. We directly constrain the full 3 + 1 active-sterile mixing matrix elements vertical bar U-alpha 4 vertical bar(2) , with alpha is an element of (e,mu,tau), and the mass-squared splitting Delta m(41)(2) (math) 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 coupled to only 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 datasets. The exact results are slightly prior dependent, but we reliably find all matrix elements to be constrained below vertical bar U-alpha 4 vertical bar(2) less than or similar to 10(-3) . Short-baseline neutrino oscillation hints in favor of eV-scale sterile neutrinos arc 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 nu beta beta 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% CL, more stringent than the limits from current laboratory experiments.
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Ternes, C. A., Gariazzo, S., Hajjar, R., Mena, O., Sorel, M., & Tortola, M. (2019). Neutrino mass ordering at DUNE: An extra nu bonus. Phys. Rev. D, 100(9), 093004–10pp.
Abstract: 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 operational. 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 ideal ingredients to extract the neutrino mass ordering via matter effects in the neutrino propagation through Earth. Crucially, muon capture by argon provides excellent charge tagging, allowing us to disentangle the neutrino and antineutrino signature. This is an important extra benefit of having a liquid argon time projection chamber as a far detector, that could render an similar to 3.5 sigma extraction of the mass ordering after approximately 7 yr of exposure.
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Gariazzo, S., & Mena, O. (2019). Cosmology-marginalized approaches in Bayesian model comparison: The neutrino mass as a case study. Phys. Rev. D, 99(2), 021301–6pp.
Abstract: We propose here a novel method which singles out the a priori unavoidable dependence on the underlying cosmological model when extracting parameter constraints, providing robust limits which only depend on the considered dataset. Interestingly, when dealing with several possible cosmologies and interpreting the Bayesian preference in terms of the Gaussian statistical evidence, the preferred model is much less favored than when only two cases are compared. As a working example, we apply our approach to the cosmological neutrino mass bounds, which play a fundamental role not only in establishing the contribution of relic neutrinos to the dark matter of the Universe but also in the planning of future experimental searches of the neutrino character and of the neutrino mass ordering.
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Witte, S., Villanueva-Domingo, P., Gariazzo, S., Mena, O., & Palomares-Ruiz, S. (2018). EDGES result versus CMB and low-redshift constraints on ionization histories. Phys. Rev. D, 97(10), 103533–8pp.
Abstract: We examine the results from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), which has recently claimed the detection of a strong absorption in the 21 cm hyperfine transition line of neutral hydrogen, at redshifts demarcating the early stages of star formation. More concretely, we study the compatibility of the shape of the EDGES absorption profile, centered at a redshift of z similar to 17.2, with measurements of the reionization optical depth, the Gunn-Peterson optical depth, and Lyman-alpha emission from star-forming galaxies, for a variety of possible reionization models within the standard ACDM framework (that is, a Universe with a cosmological constant. and cold dark matter CDM). When, conservatively, we only try to accommodate the location of the absorption dip, we identify a region in the parameter space of the astrophysical parameters that successfully explains all of the aforementioned observations. However, one of the most abnormal features of the EDGES measurement is the absorption amplitude, which is roughly a factor of 2 larger than the maximum allowed value in the ACDM framework. We point out that the simple considered astrophysical models that produce the largest absorption amplitudes are unable to explain the depth of the dip and of reproducing the observed shape of the absorption profile.
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Gariazzo, S., Escudero, M., Diamanti, R., & Mena, O. (2017). Cosmological searches for a noncold dark matter component. Phys. Rev. D, 96(4), 043501–11pp.
Abstract: We explore an extended cosmological scenario where the dark matter is an admixture of cold and additional noncold species. The mass and temperature of the noncold dark matter particles are extracted from a number of cosmological measurements. Among others, we consider tomographic weak lensing data and Milky Way dwarf satellite galaxy counts. We also study the potential of these scenarios in alleviating the existing tensions between local measurements and cosmic microwave background ( CMB) estimates of the S-8 parameter, with S-8 = sigma(8)root Omega(m), and of the Hubble constant H-0. In principle, a subdominant, noncold dark matter particle with a mass m(X) similar to keV, could achieve the goals above. However, the preferred ranges for its temperature and its mass are different when extracted from weak lensing observations and from Milky Way dwarf satellite galaxy counts, since these two measurements require suppressions of the matter power spectrum at different scales. Therefore, solving simultaneously the CMB-weak lensing tensions and the small scale crisis in the standard cold dark matter picture via only one noncold dark matter component seems to be challenging.
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Gariazzo, S., Mena, O., Miralles, V., Ramirez, H., & Boubekeur, L. (2017). Running of featureful primordial power spectra. Phys. Rev. D, 95(12), 123534–7pp.
Abstract: Current measurements of the temperature and polarization anisotropy power spectra of the cosmic microwave background (CMB) seem to indicate that the naive expectation for the slow-roll hierarchy within the most simple inflationary paradigm may not be respected in nature. We show that a primordial power spectrum with localized features could in principle give rise to the observed slow-roll anarchy when fitted to a featureless power spectrum. From a model comparison perspective, and assuming that nature has chosen a featureless primordial power spectrum, we find that, while with mock Planck data there is only weak evidence against a model with localized features, upcoming CMB missions may provide compelling evidence against such a nonstandard primordial power spectrum. This evidence could be reinforced if a featureless primordial power spectrum is independently confirmed from bispectrum and/or galaxy clustering measurements.
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Di Valentino, E., Gariazzo, S., Gerbino, M., Giusarma, E., & Mena, O. (2016). Dark radiation and inflationary freedom after Planck 2015. Phys. Rev. D, 93(8), 083523–28pp.
Abstract: The simplest inflationary models predict a primordial power spectrum (PPS) of the curvature fluctuations that can be described by a power-law function that is nearly scale invariant. It has been shown, however, that the low-multipole spectrum of the cosmic microwave background anisotropies may hint at the presence of some features in the shape of the scalar PPS, which could deviate from its canonical power-law form. We study the possible degeneracies of this nonstandard PPS with the active neutrino masses, the effective number of relativistic species, and a sterile neutrino or a thermal axion mass. The limits on these additional parameters are less constraining in a model with a nonstandard PPS when including only the temperature autocorrelation spectrum measurements in the data analyses. The inclusion of the polarization spectra noticeably helps in reducing the degeneracies, leading to results that typically show no deviation from the Lambda CDM model with a standard power-law PPS. These findings are robust against changes in the function describing the noncanonical PPS. Albeit current cosmological measurements seem to prefer the simple power-law PPS description, the statistical significance to rule out other possible parametrizations is still very poor. Future cosmological measurements are crucial to improve the present PPS uncertainties.
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Gariazzo, S., Lopez-Honorez, L., & Mena, O. (2015). Primordial power spectrum features and f(NL) constraints. Phys. Rev. D, 92(6), 063510–12pp.
Abstract: The simplest models of inflation predict small non-Gaussianities and a featureless power spectrum. However, there exist a large number of well-motivated theoretical scenarios in which large non-Gaussianties could be generated. In general, in these scenarios the primordial power spectrum will deviate from its standard power law shape. We study, in a model-independent manner, the constraints from future large-scale structure surveys on the local non-Gaussianity parameter f(NL) when the standard power law assumption for the primordial power spectrum is relaxed. If the analyses are restricted to the large-scale-dependent bias induced in the linear matter power spectrum by non-Gaussianites, the errors on the f(NL) parameter could be increased by 60% when exploiting data from the future DESI survey, if dealing with only one possible dark matter tracer. In the same context, a nontrivial bias vertical bar delta f(NL)vertical bar similar to 2.5 could be induced if future data are fitted to the wrong primordial power spectrum. Combining all the possible DESI objects slightly ameliorates the problem, as the forecasted errors on f(NL) would be degraded by 40% when relaxing the assumptions concerning the primordial power spectrum shape. Also, the shift on the non-Gaussianity parameter is reduced in this case, vertical bar delta f(NL)vertical bar similar to 1.6. The addition of cosmic microwave background priors ensures robust future f(NL) bounds, as the forecasted errors obtained including these measurements are almost independent on the primordial power spectrum features, and vertical bar delta f(NL)vertical bar similar to 0.2, close to the standard single-field slow-roll paradigm prediction.
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Di Valentino, E., Gariazzo, S., Giusarma, E., & Mena, O. (2015). Robustness of cosmological axion mass limits. Phys. Rev. D, 91(12), 123505–12pp.
Abstract: We present the cosmological bounds on the thermal axion mass in an extended cosmological scenario in which the primordial power spectrum of scalar perturbations differs from the usual power-law shape predicted by the simplest inflationary models. The power spectrum is instead modeled by means of a “piecewise cubic Hermite interpolating polynomial” (PCHIP). When using cosmic microwave background measurements combined with other cosmological data sets, the thermal axion mass constraints are degraded only slightly. The addition of the measurements of sigma(8) and Omega(m) from the 2013 Planck cluster catalog on galaxy number counts relaxes the bounds on the thermal axion mass, mildly favoring a similar to 1 eV axion mass, regardless of the model adopted for the primordial power spectrum. However, in general, such a preference disappears if the sum of the three active neutrino masses is also considered as a free parameter in our numerical analyses, due to the strong correlation between the masses of these two hot thermal relics.
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Gariazzo, S. (2020). Constraining power of open likelihoods, made prior-independent. Eur. Phys. J. C, 80(6), 552–6pp.
Abstract: One of the most criticized features of Bayesian statistics is the fact that credible intervals, especially when open likelihoods are involved, may strongly depend on the prior shape and range. Many analyses involving open likelihoods are affected by the eternal dilemma of choosing between linear and logarithmic prior, and in particular in the latter case the situation is worsened by the dependence on the prior range under consideration. In this letter, we revive a simple method to obtain constraints that depend neither on the prior shape nor range and, using the tools of Bayesian model comparison, extend it to overcome the possible dependence of the bounds on the choice of free parameters in the numerical analysis. An application to the case of cosmological bounds on the sum of the neutrino masses is discussed as an example.
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