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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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Giusarma, E., Di Valentino, E., Lattanzi, M., Melchiorri, A., & Mena, O. (2014). Relic neutrinos, thermal axions, and cosmology in early 2014. Phys. Rev. D, 90(4), 043507–17pp.
Abstract: We present up-to-date cosmological bounds on the sum of active neutrino masses as well as on extended cosmological scenarios with additional thermal relics, as thermal axions or sterile neutrino species. Our analyses consider all the current available cosmological data in the beginning of year 2014, including the very recent and most precise baryon acoustic oscillation measurements from the Baryon Oscillation Spectroscopic Survey. In the minimal three-active-neutrino scenario, we find Sigma m(nu) < 0.22 eV at 95% C.L. from the combination of cosmic microwave background (CMB), baryon acoustic oscillation, and Hubble Space Telescope measurements of the Hubble constant. A nonzero value for the sum of the three active neutrino masses of similar to 0.3 eV is significantly favored at more than three standard deviations when adding the constraints on s 8 and Om from the Planck cluster catalog on galaxy number counts. This preference for nonzero thermal relic masses disappears almost completely in both the thermal axion and massive sterile neutrino schemes. Extra light species contribute to the effective number of relativistic degrees of freedom, parametrized via N-eff. We found that when the recent detection of B mode polarization from the BICEP2 experiment is considered, an analysis of the combined CMB data in the framework of LCDM + r models gives N-eff = 3.90 +/- 0.42, suggesting the presence of an extra relativistic relic at more than 95% C.L. from CMB-only data.
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Boubekeur, L., Giusarma, E., Mena, O., & Ramirez, H. (2014). Current status of modified gravity. Phys. Rev. D, 90(10), 103512–10pp.
Abstract: We revisit the cosmological viability of the Hu-Sawicki modified gravity scenario. The impact of such a modification on the different cosmological observables, including gravitational waves, is carefully described. The most recent cosmological data, as well as constraints on the relationship between the clustering parameter sigma(8) and the current matter mass-energy density Omega(m) from cluster number counts and weak lensing tomography, are considered in our numerical calculations. The strongest bound we find is vertical bar f(R0)vertical bar < 3.7 x 10(-6) at 95% C.L. Forthcoming cluster surveys covering 10 000 deg(2) in the sky, with galaxy surface densities of O(10) arcmin(-2) could improve the precision in the sigma(8)-Omega(m) relationship, tightening the above constraint.
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Gerbino, M., Freese, K., Vagnozzi, S., Lattanzi, M., Mena, O., Giusarma, E., et al. (2017). Impact of neutrino properties on the estimation of inflationary parameters from current and future observations. Phys. Rev. D, 95(4), 043512–22pp.
Abstract: We study the impact of assumptions about neutrino properties on the estimation of inflationary parameters from cosmological data, with a specific focus on the allowed contours in the n(s)/r plane, where n(s) is the scalar spectral index and r is the tensor-to-scalar ratio. We study the following neutrino properties: (i) the total neutrino mass M-i = Sigma(i)m(i) (where the index i = 1, 2, 3 runs over the three neutrino mass eigenstates); (ii) the number of relativistic degrees of freedom N-eff at the time of recombination; and (iii) the neutrino hierarchy. Whereas previous literature assumed three degenerate neutrino masses or two massless neutrino species (approximations that clearly do not match neutrino oscillation data), we study the cases of normal and inverted hierarchy. Our basic result is that these three neutrino properties induce < 1 sigma shift of the probability contours in the n(s)/r plane with both current or upcoming data. We find that the choice of neutrino hierarchy (normal, inverted, or degenerate) has a negligible impact. However, the minimal cutoff on the total neutrino mass M-v,M-min = 0 that accompanies previous works using the degenerate hierarchy does introduce biases in the n(s)/r plane and should be replaced by M-v,M-min = 0.059 eV as required by oscillation data. Using current cosmic microwave background (CMB) data from Planck and Bicep/Keck, marginalizing over the total neutrino mass M-v and over r can lead to a shift in the mean value of ns of similar to 0.3 sigma toward lower values. However, once baryon acoustic oscillation measurements are included, the standard contours in the n(s)/r plane are basically reproduced. Larger shifts of the contours in the n(s)/r plane (up to 0.8 sigma) arise for nonstandard values of N-eff. We also provide forecasts for the future CMB experiments Cosmic Origins Explorer (COrE, satellite) and Stage-IV (ground-based) and show that the incomplete knowledge of neutrino properties, taken into account by a marginalization over M-v, could induce a shift of similar to 0.4 sigma toward lower values in the determination of ns (or a similar to 0.8 sigma shift if one marginalizes over N-eff). Comparison to specific inflationary models is shown. Imperfect knowledge of neutrino properties must be taken into account properly, given the desired precision in determining whether or not inflationary models match the future data.
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