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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Lopez-Honorez, L., Mena, O., Palomares-Ruiz, S., & Villanueva-Domingo, P. (2017). Warm dark matter and the ionization history of the Universe. Phys. Rev. D, 96(10), 103539–14pp.
Abstract: In warm dark matter scenarios structure formation is suppressed on small scales with respect to the cold dark matter case, reducing the number of low-mass halos and the fraction of ionized gas at high redshifts and thus, delaying reionization. This has an impact on the ionization history of the Universe and measurements of the optical depth to reionization, of the evolution of the global fraction of ionized gas and of the thermal history of the intergalactic medium, can be used to set constraints on the mass of the dark matter particle. However, the suppression of the fraction of ionized medium in these scenarios can be partly compensated by varying other parameters, as the ionization efficiency or the minimum mass for which halos can host star-forming galaxies. Here we use different data sets regarding the ionization and thermal histories of the Universe and, taking into account the degeneracies from several astrophysical parameters, we obtain a lower bound on the mass of thermal warm dark matter candidates of m(X) > 1.3 keV, or m(s) > 5.5 keV for the case of sterile neutrinos nonresonantly produced in the early Universe, both at 90% confidence level.
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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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Di Valentino, E., Melchiorri, A., & Mena, O. (2017). Can interacting dark energy solve the H-0 tension? Phys. Rev. D, 96(4), 043503–11pp.
Abstract: The answer is yes. We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant H-0 between the cosmic microwave background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two data sets points toward a nonzero dark matter-dark energy coupling. at more than two standard deviations, with xi = -0.26(-0.12)(+0.16) at 95% C.L., i.e. with a moderate evidence for interacting dark energy with an odds ratio of 6:1 respect to a non interacting cosmological constant. However the H-0 tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantomlike equation of state w = -1.185 +/- 0.064 (at 68% C.L.), ruling out the pure cosmological constant case, w = -1, again at more than two standard deviations. When Planck data are combined with external datasets, as BAO, JLA Supernovae Ia luminosity distances, cosmic shear or lensing data, we find perfect consistency with the cosmological constant scenario and no compelling evidence for a dark matter-dark energy coupling.
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Villanueva-Domingo, P., Gnedin, N. Y., & Mena, O. (2018). Warm Dark Matter and Cosmic Reionization. Astrophys. J., 852(2), 139–7pp.
Abstract: In models with dark matter made of particles with keV masses, such as a sterile neutrino, small-scale density perturbations are suppressed, delaying the period at which the lowest mass galaxies are formed and therefore shifting the reionization processes to later epochs. In this study, focusing on Warm Dark Matter (WDM) with masses close to its present lower bound, i.e., around the 3. keV region, we derive constraints from galaxy luminosity functions, the ionization history and the Gunn-Peterson effect. We show that even if star formation efficiency in the simulations is adjusted to match the observed UV galaxy luminosity functions in both CDM and WDM models, the full distribution of Gunn-Peterson optical depth retains the strong signature of delayed reionization in the WDM model. However, until the star formation and stellar feedback model used in modern galaxy formation simulations is constrained better, any conclusions on the nature of dark matter derived from reionization observables remain model-dependent.
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