Yvonne Y. Y. Wong

Cosmology Favoring Extra Radiation and Sub-eV Mass Sterile Neutrinos as an Option

Jan Hamann, Steen Hannestad, Georg G. Raffelt, Irene Tamborra, 3, 4 and Yvonne Y. Y. Wong Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Föhringer Ring 6, 80805 München, Germany Dipartimento Interateneo di Fisica “Michelangelo Merlin”, Via Amendola 173, 70126 Bari, Italy INFN, Sezione di Bari, Via Orabona 4, 70126 Bari, Italy Institut für Theoretische Teilchenphysik und Kosmologie, RWTH Aachen, 52056 Aachen, Germany (Dated: 25 June 2010, revised 23 September 2010)

Probing cosmological parameters with the CMB: Forecasts from Monte Carlo simulations

The Fisher matrix formalism has in recent times become the standard method for predicting the precision with which various cosmological parameters can be extracted from future data. This approach is fast and generally returns accurate estimates for the parameter errors when the individual parameter likelihoods approximate a Gaussian distribution. However, where Gaussianity is not respected (due, for instance, to strong parameter degeneracies), the Fisher matrix formalism loses its reliability. In this paper, we compare the results of the Fisher matrix approach with those from Monte Carlo simulations. The latter method is based on the publicly available CosmoMC code, but uses synthetic realizations of data sets anticipated for future experiments. We focus on prospective cosmic microwave background (CMB) data from the Planck satellite, with or without CMB lensing information, and its implications for a minimal cosmological scenario with eight parameters and an extended model with eleven parameters. We show that in many cases, the projected sensitivities from the Fisher matrix and the Monte Carlo methods differ significantly, particularly for models with many parameters. Sensitivities to the neutrino mass and the dark matter fraction are especially susceptible to change.

Analytical treatment of neutrino asymmetry equilibration from flavor oscillations in the early universe

A recent numerical study by A. D. Dolgov, S. H. Hansen, S. Pastor, S. T. Petcov, G. G. Raffelt, and D. V. Semikoz (DHPPRS) [Nucl. Phys. B632, 363 (2002)] found that complete or partial equilibrium between all active neutrino flavors can be achieved before the big bang nucleosynthesis epoch via flavor oscillations, if the oscillation parameters are those inferred from the atmospheric and solar neutrino data, and, in some cases, if

Cosmological and Astrophysical Neutrino Mass Measurements

{\ensuremath{\theta}}_{13}

Sterile neutrinos with eV masses in cosmology — How disfavoured exactly?

is also sizable. As such, cosmological constraints on the electron neutrino-antineutrino asymmetry are now applicable in all three neutrino sectors. In the present work, we provide an analytical treatment of the scenarios considered in DHPPRS, and demonstrate that their results are stable even for very large initial asymmetries. The equilibration mechanism can be understood in terms of a Mikheyev-Smirnov-Wolfenstein-like effect for a maximally mixed and effectively monochromatic system. We also comment on the DHPPRSs choices of mixing parameters, and their handling of collisional effects, both of which could impinge on the extent of flavor equilibrium.

Measuring neutrino masses and dark energy with weak lensing tomography

Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.

Cosmological parameters from large scale structure - geometric versus shape information

We study cosmological models that contain sterile neutrinos with eV-range masses as suggested by reactor and short-baseline oscillation data. We confront these models with both precision cosmological data (probing the CMB decoupling epoch) and light-element abundances (probing the BBN epoch). In the minimal ΛCDM model, such sterile neutrinos are strongly disfavoured by current data because they contribute too much hot dark matter. However, if the cosmological framework is extended to include also additional relativistic degrees of freedom beyond the three standard neutrinos and the putative sterile neutrinos, then the hot dark matter constraint on the sterile states is considerably relaxed. A further improvement is achieved by allowing a dark energy equation of state parameter w < −1. While BBN strongly disfavours extra radiation beyond the assumed eV-mass sterile neutrino, this constraint can be circumvented by a small νe degeneracy. Any model containing eV-mass sterile neutrinos implies also strong modifications of other cosmological parameters. Notably, the inferred cold dark matter density can shift up by 20–75% relative to the standard ΛCDM value.

Neutrino and axion hot dark matter bounds after WMAP-7

Surveys of weak gravitational lensing of distant galaxies will be one of the key cosmological probes in the future. We study the ability of such surveys to constrain neutrino masses and the equation of state parameter of dark energy, focusing on how tomographic information can improve the sensitivity to these parameters. We also provide a detailed discussion of systematic effects pertinent to weak lensing surveys, and the possible degradation of sensitivity to cosmological parameters due to these effects. For future probes such as the Large Synoptic Survey Telescope survey, we find that, when combined with cosmic microwave background data from the Planck satellite, a sensitivity to neutrino masses of can be reached. These results are not affected by variations in the running of the scalar spectral index, the time-dependence of the dark energy equation of state, and/or the number of relativistic degrees of freedom.

Neutrino Mass in Cosmology: Status and Prospects

The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of these two types of information on cosmological parameter estimation for current data, and show that for the simplest cosmological models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features. An immediate corollary is that contrary to popular beliefs, the upper limit on the neutrino mass m(nu) presently derived from LSS combined with cosmic microwave background (CMB) data does not in fact arise from the possible small-scale power suppression due to neutrino free-streaming, if we limit the model framework to minimal Lambda CDM+m(nu). However, in more complicated models, such as those extended with extra light degrees of freedom and a dark energy equation of state parameter w differing from -1, shape information becomes crucial for the resolution of parameter degeneracies. This conclusion will remain true even when data from the Planck spacecraft are combined with SDSS DR7 data. In the course of our analysis, we update both the BAO likelihood function by including an exact numerical calculation of the time of decoupling, as well as the HPS likelihood, by introducing a new dewiggling procedure that generalises the previous approach to models with an arbitrary sound horizon at decoupling. These changes allow a consistent application of the BAO and HPS data sets to a much wider class of models, including the ones considered in this work. All the cases considered here are compatible with the conservative 95%-bounds Sigma m(nu) < 1.16 eV, N-eff = 4.8 +/- 2.0.

Dark energy properties from large future galaxy surveys

We update cosmological hot dark matter constraints on neutrinos and hadronic axions. Our most restrictive limits use 7-year data from the Wilkinson Microwave Anisotropy Probe for the cosmic microwave background anisotropies, the halo power spectrum (HPS) from the 7th data release of the Sloan Digital Sky Survey, and the Hubble constant from Hubble Space Telescope observations. We find 95% C.L. upper limits of \sum m_\nu<0.44 eV (no axions), m_a<0.91 eV (assuming \sum m_\nu=0), and \sum m_\nu<0.41 eV and m_a<0.72 eV for two hot dark matter components after marginalising over the respective other mass. CMB data alone yield \sum m_\nu<1.19 eV (no axions), while for axions the HPS is crucial for deriving m_a constraints. This difference can be traced to the fact that for a given hot dark matter fraction axions are much more massive than neutrinos.