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Centelles Chulia, S., Ma, E., Srivastava, R., & Valle, J. W. F. (2017). Dirac neutrinos and dark matter stability from lepton quarticity. Phys. Lett. B, 767, 209–213.
Abstract: We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type-I seesaw mechanism as a result of a Z(4) discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos.
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Giusarma, E., Gerbino, M., Mena, O., Vagnozzi, S., Ho, S., & Freese, K. (2016). Improvement of cosmological neutrino mass bounds. Phys. Rev. D, 94(8), 083522–8pp.
Abstract: The most recent measurements of the temperature and low-multipole polarization anisotropies of the cosmic microwave background from the Planck satellite, when combined with galaxy clustering data from the Baryon Oscillation Spectroscopic Survey in the form of the full shape of the power spectrum, and with baryon acoustic oscillation measurements, provide a 95% confidence level (C.L.) upper bound on the sum of the three active neutrinos Sigma m(nu) < 0.183 eV, among the tightest neutrino mass bounds in the literature, to date, when the same data sets are taken into account. This very same data combination is able to set, at similar to 70% C.L., an upper limit on Sigma m(nu) of 0.0968 eV, a value that approximately corresponds to the minimal mass expected in the inverted neutrino mass hierarchy scenario. If high-multipole polarization data from Planck is also considered, the 95% C.L. upper bound is tightened to Sigma m(nu) < 0.176 eV. Further improvements are obtained by considering recent measurements of the Hubble parameter. These limits are obtained assuming a specific nondegenerate neutrino mass spectrum; they slightly worsen when considering other degenerate neutrino mass schemes. Low-redshift quantities, such as the Hubble constant or the reionization optical depth, play a very important role when setting the neutrino mass constraints. We also comment on the eventual shifts in the cosmological bounds on Sigma m(nu) when possible variations in the former two quantities are addressed.
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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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Di Valentino, E., Giusarma, E., Mena, O., Melchiorri, A., & Silk, J. (2016). Cosmological limits on neutrino unknowns versus low redshift priors. Phys. Rev. D, 93(8), 083527–11pp.
Abstract: Recent cosmic microwave background (CMB) temperature and polarization anisotropy measurements from the Planck mission have significantly improved previous constraints on the neutrino masses as well as the bounds on extended models with massless or massive sterile neutrino states. However, due to parameter degeneracies, additional low redshift priors are mandatory in order to sharpen the CMB neutrino bounds. We explore here the role of different priors on low redshift quantities, such as the Hubble constant, the cluster mass bias, and the reionization optical depth tau. Concerning current priors on the Hubble constant and the cluster mass bias, the bounds on the neutrino parameters may differ appreciably depending on the choices adopted in the analyses. With regard to future improvements in the priors on the reionization optical depth, a value of tau = 0.05 +/- 0.01, motivated by astrophysical estimates of the reionization redshift, would lead to Sigma m(nu) < 0.0926 eV at 90% C.L., when combining the full Planck measurements, baryon acoustic oscillation, and Planck clusters data, thereby opening the window to unravel the neutrino mass hierarchy with existing cosmological probes.
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Di Valentino, E., Giusarma, E., Lattanzi, M., Mena, O., Melchiorri, A., & Silk, J. (2016). Cosmological axion and neutrino mass constraints from Planck 2015 temperature and polarization data. Phys. Lett. B, 752, 182–185.
Abstract: Axions currently provide the most compelling solution to the strong CP problem. These particles may be copiously produced in the early universe, including via thermal processes. Therefore, relic axions constitute a hot dark matter component and their masses are strongly degenerate with those of the three active neutrinos, as they leave identical signatures in the different cosmological observables. In addition, thermal axions, while still relativistic states, also contribute to the relativistic degrees of freedom, parameterized via N-eff. We present the cosmological bounds on the relic axion and neutrino masses, exploiting the full Planck mission data, which include polarization measurements. In the mixed hot dark matter scenario explored here, we find the tightest and more robust constraint to date on the sum of the three active neutrino masses, Sigma m nu < 0.136eV at 95% CL, as it is obtained in the very well-known linear perturbation regime. The Planck Sunyaev-Zeldovich cluster number count data further tightens this bound, providing a 95% CL upper limit of Sigma m nu < 0.126 eV in this very same mixed hot dark matter model, a value which is very close to the expectations in the inverted hierarchical neutrino mass scenario. Using this same combination of data sets we find the most stringent bound to date on the thermal axion mass, m(a) < 0.529 eV at 95% CL.
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