49 research outputs found
Inflation with primordial broken power law spectrum as an alternative to the concordance cosmological model
No full textWe consider cosmological models with a non-scale-invariant spectrum of primordial perturbations and assess whether they represent a viable alternative to the concordance Lambda CDM model. We find that in the framework of a model selection analysis, the WMAP and 2dF data do not provide any conclusive evidence in favor of one or the other kind of model. However, when a marginalization over the entire space of nuisance parameters is performed, models with a modified primordial spectrum and Omega(A) = 0 are strongly disfavored
Cosmic Dark Radiation and Neutrinos
No full textNew measurements of the cosmic microwave background (CMB) by the Planck mission have greatly increased our knowledge about the universe. Dark radiation, a weakly interacting component of radiation, is one of the important ingredients in our cosmological model which is testable by Planck and other observational probes. At the moment, the possible existence of dark radiation is an unsolved question. For instance, the discrepancy between the value of the Hubble constant, H0, inferred from the Planck data and local measurements of H0 can to some extent be alleviated by enlarging the minimal ΛCDM model to include additional relativistic degrees of freedom. From a fundamental physics point of view, dark radiation is no less interesting. Indeed, it could well be one of the most accessible windows to physics beyond the standard model, for example, sterile neutrinos. Here, we review the most recent cosmological results including a complete investigation of the dark radiation sector in order to provide an overview of models that are still compatible with new cosmological observations. Furthermore, we update the cosmological constraints on neutrino physics and dark radiation properties focusing on tensions between data sets and degeneracies among parameters that can degrade our information or mimic the existence of extra species
Axion cold dark matter: Status after Planck and BICEP2
No full textWe investigate the axion dark matter scenario (ADM), in which axions account for all of the dark matter in the Universe, in light of the most recent cosmological data. In particular, we use the Planck temperature data, complemented by WMAP E-polarization measurements, as well as the recent BICEP2 observations of B-modes. Baryon acoustic oscillation data, including those from the baryon oscillation spectroscopic survey, are also considered in the numerical analyses. We find that, in the minimal ADM scenario and for Delta(QCD) = 200 MeV, the full data set implies that the axion mass m(a) = 82.2 +/- 1.1 μeV [corresponding to the Peccei-Quinn symmetry being broken at a scale f(a) = (7.54 +/- 0.10) x 10(10) GeV], or m(a) = 76.6 +/- 2.6 μeV [f(a) = (8.08 +/- 0.27) x 10(10) GeV] when we allow for a nonstandard effective number of relativistic species N-eff. We also find a 2 sigma preference for N-eff > 3.046. The limit on the sum of neutrino masses is Sigma m(v) < 0.25 eV at 95% C.L. for N-eff = 3.046, or Sigma m(v) < 0.47 eV when N-eff is a free parameter. Considering extended scenarios where either the dark energy equation-of-state parameter w, the tensor spectral index n(t), or the running of the scalar index dn(s)/d ln k is allowed to vary does not change significantly the axion mass-energy density constraints. However, in the case of the full data set exploited here, there is a preference for a nonzero tensor index or scalar running, driven by the different tensor amplitudes implied by the Planck and BICEP2 observations. We also study the effect on our estimates of theoretical uncertainties, in particular the imprecise knowledge of the QCD scale Delta(QCD), in the calculation of the temperature-dependent axion mass. We find that in the simplest ADM scenario the Planck + WP data set implies that the axion mass m(a) = 63.7 +/- 1.2 μeV for Delta(QCD) = 400 MeV. We also comment on the possibility that axions do not make up for all the dark matter, or that the contribution of string-produced axions has been grossly underestimated; in that case, the values that we find for the mass can conservatively be considered as lower limits. Dark matter axions with mass in the 60-80 μeV (corresponding to an axion-photon coupling G(a gamma gamma) similar to 10(-14) GeV-1) range can, in principle, be detected by looking for axion-to-photon conversion occurring inside a tunable microwave cavity permeated by a high-intensity magnetic field, and operating at a frequency nu similar or equal to 15-20 GHz. This is out of the reach of current experiments like the axion dark matter experiment (limited to a maximum frequency of a few GHzs), but is, on the other hand, within the reach of the upcoming axion dark matter experiment-high frequency experiment that will explore the 4-40 GHz frequency range and then be sensitive to axion masses up to similar to 160 μeV
Relic neutrinos, thermal axions, and cosmology in early 2014
No full textWe 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
Constraints on massive sterile neutrino species from current and future cosmological data
No full textSterile massive neutrinos are a natural extension of the standard model of elementary particles. The energy density of the extra sterile massive states affects cosmological measurements in an analogous way to that of active neutrino species. We perform here an analysis of current cosmological data and derive bounds on the masses of the active and the sterile neutrino states, as well as on the number of sterile states. The so-called (3 + 2) models, with three sub-eV active massive neutrinos plus two sub-eV massive sterile species, is well within the 95% CL allowed regions when considering cosmological data only. If the two extra sterile states have thermal abundances at decoupling, big bang nucleosynthesis bounds compromise the viability of (3 + 2) models. Forecasts from future cosmological data on the active and sterile neutrino parameters are also presented. Independent measurements of the neutrino mass from tritium beta-decay experiments and of the Hubble constant could shed light on sub-eV massive sterile neutrino scenarios
Impact of general reionization scenarios on extraction of inflationary parameters
No full textDetermination of whether the Harrison-Zel'dovich spectrum for primordial scalar perturbations is consistent with observations is sensitive to assumptions about the reionization scenario. In light of this result, we revisit constraints on inflationary models using more general reionization scenarios. While the bounds on the tensor-to-scalar ratio are largely unmodified, when different reionization schemes are addressed, hybrid models are back into the inflationary game. In the general reionization picture, we reconstruct both the shape and amplitude of the inflaton potential. We discuss how relaxing the simple reionization restriction affects the reconstruction of the potential through the changes in the constraints on the spectral index, the tensor-to-scalar ratio and the running of the spectral index. We also find that the inclusion of other Cosmic Microwave Background data in addition to the Wilkinson Microwave Anisotropy probe data excludes the very flat potentials typical of models in which the inflationary evolution reaches a late-time attractor, as a consequence of the fact that the running of the spectral index is constrained to be different from zero at 99% confidence level.We would like to thank William Kinney for useful discussion. O. M.'s work is supported by the MICINN (Spain) Ramon y Cajal Contract Nos. AYA2008-03531 and CSD2007-00060. M. P. is supported by a MEC-FPU Spanish grant.Peer reviewe
Harrison-Zel'dovich primordial spectrum is consistent with observations
No full textInflation predicts primordial scalar perturbations with a nearly scale-invariant spectrum and a spectral index approximately unity [the Harrison-Zel'dovich (HZ) spectrum]. The first important step for inflationary cosmology is to check the consistency of the HZ primordial spectrum with current observations. Recent analyses have claimed that a HZ primordial spectrum is excluded at more than 99% c. l. Here we show that the HZ spectrum is only marginally disfavored if one considers a more general reionization scenario. Data from the Planck mission will settle the issue.Peer reviewe
Exploring cosmic origins with CORE: Cosmological parameters
No full textValentino, E.D., Brinckmann, T., Gerbino, M., Poulin, V., Bouchet, F.R., Lesgourgues, J., Melchiorri, A., Chluba, J., Clesse, S., Delabrouille, J., Dvorkin, C., Forastieri, F., Galli, S., Hooper, D.C., Lattanzi, M., Martins, C.J.A.P., Salvati, L., Cabass, G., Caputo, A., Giusarma, E., Hivon, E., Natoli, P., Pagano, L., Paradiso, S., Rubiño-Martin, J.A., Achúcarro, A., Ade, P., Allison, R., Arroja, F., Ashdown, M., Ballardini, M., Banday, A.J., Banerji, R., Bartolo, N., Bartlett, J.G., Basak, S., Baumann, D., De Bernardis, P., Bersanelli, M., Bonaldi, A., Bonato, M., Borrill, J., Boulanger, F., Bucher, M., Burigana, C., Buzzelli, A., Cai, Z.-Y., Calvo, M., Carvalho, C.S., Castellano, G., Challinor, A., Charles, I., Colantoni, I., Coppolecchia, A., Crook, M., D'Alessandro, G., Petris, M.D., Zotti, G.D., Diego, J.M., Errard, J., Feeney, S., Fernandez-Cobos, R., Ferraro, S., Finelli, F., De Gasperis, G., Génova-Santos, R.T., González-Nuevo, J., Grandis, S., Greenslade, J., Hagstotz, S., Hanany, S., Handley, W., Hazra, D.K., Hernández-Monteagudo, C., Hervias-Caimapo, C., Hills, M., Kiiveri, K., Kisner, T., Kitching, T., Kunz, M., Kurki-Suonio, H., Lamagna, L., Lasenby, A., Lewis, A., Liguori, M., Lindholm, V., Lopez-Caniego, M., Luzzi, G., Maffei, B., Martin, S., Martinez-Gonzalez, E., Masi, S., Matarrese, S., McCarthy, D., Melin, J.-B., Mohr, J.J., Molinari, D., Monfardini, A., Negrello, M., Notari, A., Paiella, A., Paoletti, D., Patanchon, G., Piacentini, F., Piat, M., Pisano, G., Polastri, L., Polenta, G., Pollo, A., Quartin, M., Remazeilles, M., Roman, M., Ringeval, C., Tartari, A., Tomasi, M., Tramonte, D., Trappe, N., Trombetti, T., Tucker, C., Väliviita, J., De Weygaert, R.V., Tent, B.V., Vennin, V., Vermeulen, G., Vielva, P., Vittorio, N., Young, K., Zannoni, M
Impact of neutrino properties on the estimation of inflationary parameters from current and future observations
No full textWe 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.</p
