arXiv subjects

M. White

Publications and source records attributed to M. White.

62 records · Page 4Linked to original sources

arXiv2001

Power spectrum normalization from the local abundance of rich clusters of galaxies

The number density of rich galaxy clusters still provides the most robust way of normalizing the power spectrum of dark matter perturbations on scales relevant to large-scale structure. We revisit this constraint in light of several recent developments: (1) the availability of well-defined samples of local clusters with relatively accurate X-ray temperatures; (2) new theoretical mass functions for dark matter haloes which provide a good fit to large numerical simulations; (3) more accurate mass-temperature relations from larger catalogs of hydrodynamical simulations; (4) the requirement to consider closed as well as open and flat cosmologies to obtain full multi-parameter likelihood constraints for CMB and SNe studies. We present a new sample of clusters drawn from the literature and use this sample to obtain improved results on sigma_8, the normalization of the matter power spectrum on scales of 8 h^{-1} Mpc, as a function of the matter density and cosmological constant in a Universe with general curvature. We discuss our differences with previous work, and the remaining major sources of uncertainty. Final results on the 68 per cent confidence region, approximately independent of power spectrum shape, can be expressed as constraints on sigma at an appropriate cluster normalization scale R_Cl. We provide fitting formulas for R_Cl and sigma(R_Cl) for general cosmologies, as well as for sigma_8 as a function of cosmology and shape parameter Gamma. For flat models we find approximately sigma_8 \simeq 0.495^{+0.034}_{-0.037}) Omega_M^{-0.60} for Gamma=0.23, where the error bar is dominated by uncertainty in the mass-temperature relation.

astro-ph↗

arXiv2000

Particle-Mesh Simulations of the Lyman-Alpha Forest

Numerical hydrodynamical simulations have proven a successful means of reproducing many of the statistical properties of the Lyman-Alpha forest as measured in high redshift quasar spectra. Pseudo-hydrodynamical methods based only on simulating the dark matter component have been claimed to yield a comparable level of success. We investigate the degree to which two pseudo-methods, with and without allowing for a pseudo-gas pressure, are able to match the predictions of fully hydrodynamical plus dark matter simulations. We also address the requirements for convergence to the statistics of the spectra and the inferred properties of the Lyman-Alpha forest as a function of resolution and box size. Generally we find it is possible to reach agreement with full hydrodynamic simulations at the 10% level in the cumulative distributions of the flux and absorption line parameter statistics for readily achievable particle and grid numbers, but difficult to do much better.

astro-ph↗

arXiv1994

Structure Formation with Decaying Neutrinos

We consider the effects of a massive, unstable neutrino on the evolution of large--scale structure and anisotropies in the cosmic microwave background. Comparison with large--scale structure data allows us to rule out a wide range of masses and lifetimes for such neutrinos. We also define a range of masses and lifetimes which delay matter--radiation equality and improve the agreement with the data of Cold Dark Matter models with critical density.

astro-ph↗

arXiv1994

A First Map of the CMB at 0.5Deg Resolution

We use a Maximum Entropy technique to reconstruct a map of the microwave sky near the star Gamma Ursae Minoris, based on data from flights 2, 3 and 4 of the Millimeter-wave Anisotropy eXperiment (MAX).

astro-ph↗

arXiv1994

The COBE Normalization for Standard CDM

The COBE detection of CMB anisotropies provides the best way of fixing the amplitude of fluctuations on the largest scales. This normalization is usually given for an n=1 spectrum, including only the anisotropy caused by the Sachs- Wolfe effect. This is certainly not a good approximation for a model containing any reasonable amount of baryonic matter. In fact, even tilted S-W spectra are not a good fit to models like CDM. Here we normalize standard CDM (sCDM) to the 2-year COBE data, and quote the best amplitude in terms of the conventionally used measures of power. We also give normalizations for some specific variants of this standard model, and we indicate how the normalization depends on the assumed values of n, Omega_B and H_0. For sCDM we find =19.9\pm1.5uK, corresponding to sigma_8=1.34\pm0.10, with the normalization at large scales being B=(8.16\pm1.04)\times10^5 (Mpc/h)^4, and other numbers given in the Table. The measured rms temperature fluctuation smoothed on 10deg is a little low relative to this normalization. This is mainly due to the low quadrupole in the data: when the quadrupole is removed, the measured value of sigma(10) is quite consistent with the best-fitting . The use of should be preferred over sigma(10), when its value can be determined for a particular theory, since it makes full use of the data.

astro-ph↗

arXiv1993

Are SP91 and COBE Inconsistent with Cold Dark Matter?

We present results on the consistency of standard cold dark matter (CDM) models with both the COBE normalization and the data from the 4th channel of the 9-point South Pole scan. We find that CDM models are consistent with both experiments, a conclusion which is at odds with some other analyses. This is partly due to our careful treatment of the temperature autocorrelation function, but also derives from a realization that the statistical conclusions depend strongly on assumptions about the prior distribution for the normalization $Q$.

astro-ph↗

arXiv1992

Grand Unification, Gravitational Waves, and the Cosmic Microwave Background Anisotropy

We re-examine the gravitational wave background resulting from inflation and its effect on the cosmic microwave background radiation. The new COBE measurement of a cosmic background quadrupole anisotropy places an upper limit on the vacuum energy during inflation of $\approx 5 \times 10^{16}$ GeV. A stochastic background of gravitational waves from inflation could produce the entire observed signal (consistent with the observed dipole anisotropy and a flat spectrum) if the vacuum energy during inflation was as small as $1.5 \times 10^{16}$ GeV at the 95\% confidence level. This coincides nicely with the mass scale for Grand Unification inferred from precision measurements of the electroweak and strong coupling constants, for the SUSY Grand Unified Theories. Thus COBE could be providing the first direct evidence, via gravitational waves, for GUTs, and supersymmetry. Further tests of this possibility are examined, based on analyzing the energy density associated with gravitational waves from inflation.

hep-ph↗

arXiv1992

Solar Neutrino Data and Its Implications

The complete and concurrent Homestake and Kamiokande solar neutrino data sets (including backgrounds), when compared to detailed model predictions, provide no unambiguous indication of the solution to the solar neutrino problem. All neutrino-based solutions, including time-varying models, provide reasonable fits to both the 3 year concurrent data and the full 20 year data set. A simple constant B neutrino flux reduction is ruled out at greater than the 4$σ$ level for both data sets. While such a flux reduction provides a marginal fit to the unweighted averages of the concurrent data, it does not provide a good fit to the average of the full 20 year sample. Gallium experiments may not be able to distinguish between the currently allowed neutrino-based possibilities.

hep-ph↗