7201698
Flux-averaging Analysis of Type Ia Supernova Data
Because of flux conservation, flux-averaging justifies the use of the distance-redshift relation for a smooth universe in the analysis of Type Ia supernova (SN Ia) data. We have combined the SN Ia data from the High-z SN Search and the Supernova Cosmology Project and binned the combined data by flux-averaging in redshift intervals of Δz = 0.05 and Δz = 0.1. We find that the unbinned data yield a Hubble constant of H0 = 65 ± 1 km s-1 Mpc-1 (statistical error only), a matter density fraction of Ωm = 0.7 ± 0.4, and a vacuum energy density fraction of ΩΛ = 1.2 ± 0.5. The binned data for Δz = 0.1 yield H0 = 65 ± 1 km s-1 Mpc-1 (statistical error only), Ωm = 0.3 ± 0.6, and ΩΛ = 0.7 ± 0.7. Our results are not sensitive to the redshift bin size. Flux-averaging leads to less biased estimates of the cosmological parameters by reducing the bias due to systematic effects such as weak lensing. Comparison of the data of 18 SNe Ia published by both groups yields a mean SN Ia peak absolute magnitude of MB = -19.33 ± 0.25. The internal dispersion of each data set is about 0.20 mag in the calibrated SN Ia peak absolute magnitudes. The difference in analysis techniques introduces an additional uncertainty of about 0.15 mag. If the SNe Ia peak absolute luminosity changes with redshift due to evolution, our ability to measure the cosmological parameters from SN Ia data will be significantly diminished. Assuming power-law evolution in the peak absolute luminosity, (1 + z)β, we find a strong degeneracy between the evolution power-law index β and the matter density fraction Ωm. For Ωm = 0.3, we find that the unbinned data yield H0 = 65 ± 1 km s-1 Mpc-1 (statistical error only), ΩΛ = 1.4 ± 1.1, and β = 0.5 ± 1.6, and the binned data (with Δz = 0.1) yield H0 = 65 ± 1 km s-1 Mpc-1 (statistical error only), ΩΛ = 0.6 ± 1.4, and β = 0.0 ± 1.0.
1842861
Dark Energy Constraints from Baryon Acoustic Oscillations
Baryon acoustic oscillations (BAOs) in the galaxy power spectrum allow us to extract the scale of the comoving sound horizon at recombination, a cosmological standard ruler accurately determined by the cosmic microwave background anisotropy data. We examine various issues important in the use of BAOs to probe dark energy. We find that if we assume a flat universe and priors on ?m, ?mh2, and ?bh2 as expected from the Planck mission, the constraints on dark energy parameters (w0, w') scale much less steeply with survey area than (area)-1/2 for a given redshift range. The constraints on the dark energy density ?X(z), however, do scale roughly with (area)-1/2 due to the strong correlation between H(z) and ?m (which reduces the effect of priors on ?m). Dark energy constraints from BAOs are very sensitive to the assumed linear scale of matter clustering and the redshift accuracy of the survey. For a BAO survey with 0.5 ? z ? 2, ? (R) = 0.4 [corresponding to kmax (z = 0) = 0.086 h Mpc-1], and ?z/ (1 + z) = 0.001, we find = (0.115,0.183) and (0.069, 0.104) for survey areas of 1000 and 10,000 deg2, respectively. We find that it is critical to minimize the bias in the scale estimates in order to derive reliable dark energy constraints. For a 1000 (10,000) deg2 BAO survey, a 1 ? bias in ln H (z) leads to a 2 ? (3 ?) bias in w'. The bias in w' due to the same scale bias from ln DA (z) is slightly smaller and opposite in sign. The results from this paper will be useful in assessing different proposed BAO surveys and guiding the design of optimal dark energy detection strategies.
15326079
Wavelets and WMAP non-Gaussianity
We study the statistical properties of the first-year Wilkinson Microwave Anisotropy Probe (WMAP) data on different scales using the spherical Mexican hat wavelet transform. Consistent with the 2004 results of Vielva et al., we find a deviation from Gaussianity in the form of kurtosis of wavelet coefficients on 3-4 scales in the southern Galactic hemisphere. This paper extends the work of Vielva et al. as follows: We find that the non-Gaussian signal shows up more strongly in the form of a larger than expected number of cold pixels and also in the form of scale-scale correlations among wavelet coefficients. We establish the robustness of the non-Gaussian signal under more wide-ranging assumptions regarding the Galactic mask applied to the data and the noise statistics. This signal is unlikely to be due to the usual quadratic term parameterized by the nonlinearity parameter fNL. We use the skewness of the spherical Mexican hat wavelet coefficients to constrain fNL with the first-year WMAP data. Our results constrain fNL to be 50+/-80 at 68% confidence and less than 280 at 99% confidence.
42895334
Dark Energy Search with Supernovae
Abstract To determine the nature of dark energy from observational data, it is important that we use model-independent and optimal methods. We should probe dark energy using its density (allowed to be a free function of cosmic time) instead of its equation of state. We should minimize gravitational lensing effect on supernovae by flux-averaging. We need to include complementary data (for example, from the cosmic microwave background (CMB) and large scale structure (LSS)) in a consistent manner to help break the degeneracy between the dark energy density and the matter density fraction. We should push for ambitious future supernova surveys that can observe a large number of supernovae at the highest possible redshifts. I discuss these and other issues that will be important in our quest to unravel the mystery of the nature of dark energy. Current supernova, CMB, and LSS data already rule out dark energy models with dark energy densities that vary greatly with time; with the cosmological constant model providing an excellent fit to the data. A precise measurement of dark energy density as a free function of cosmic time will have a fundamental impact on particle physics and cosmology.
119244043
A robust distance measurement and dark energy constraints from the spherically averaged correlation function of Sloan Digital Sky Survey luminous red Galaxies
We measure the effective distance to z = 0.26, DV (0.26), and mh 2 from the overall shape of the spherically-averaged two-point correlati on function of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) volume-limited luminous red galaxy (LRG) sample, without assuming a dark energy model or a flat Universe. We giv e the mean and covariance matrix of DV (0.26), mh 2 , bh 2 , and ns. We show that these provide an efficient and accurate summary of the volume-limited LRG data. With flat priors on bh 2 and ns (7σWMAP7), we find mh 2 = 0.131 ± 0.020, and rs/DV (0.26) = 0.1466 +0.0068 0.0073 (the ratio of the sound horizon at the drag epoch to the effective distance to z = 0.26). We find that measurements of mh 2 or m are biased low if flux-limited (instead of volume-limited) L RG sample is used. By scaling the spherically-averaged correlation fun ction, we find the Hubble parameter H(0.26) = 79 +12 13 km s 1 Mpc 1 and the angular diameter distance DA(0.26) = 848 +86 88 Mpc. Combining our results with the cosmic microwave background and supernova data, we obtain k = 0.0059 +0.0092 0.0093 andw = 1.023 +0.054 0.053 (assuming a constant dark energy equation of state). We use LasDamas SDSS mock catalogs to compute the covariance matrix of the correlation function, and investigate the use of lognormal catal ogs as an alternative. We find that the input correlation function can be accurately recovered from lognormal catalogs, although they give larger errors on all scales (especially on small sc ales) compared to the mock catalogs derived from cosmological N-body simulations.
11940938
Constraints on generalized extended inflationary models.
We study the physical constraints on generalized extended inflationary theories, in which the Brans-Dicke field {Phi} couples to the inflaton sector in the form of two arbitrary power-law functions of {Phi}. We find that the most stringent constraints arise from the need to suppress large bubbles and from considerations of the density perturbations generated during extended inflation. We find that there are sizable portions of the parameter spaces in which all the constraints are satisfied.
118671314
Cosmic constraint to DGP brane model: Geometrical and dynamical perspectives
In this paper, the Dvali-Gabadadze-Porrati (DGP) brane model is confronted by current cosmic observational data sets from geometrical and dynamical perspectives. On the geometrical side, the recently released Union2 557 of type Ia supernovae (SN Ia), the baryon acoustic oscillation from the Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey (transverse and radial to line-of-sight data points), the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations [shift parameters R, l{sub a}(z{sub *}) and redshift at the last scatter surface z{sub *}], ages of high redshifts galaxies, i.e., the lookback time and the high redshift gamma ray bursts are used. On the dynamical side, data points about the growth function of matter linear perturbations are used. Using the same data set combination, we also constrain the flat {Lambda}CDM model as a comparison. The results show that current geometrical and dynamical observational data sets much favor the flat {Lambda}CDM model and the departure from it is above 4{sigma}(6{sigma}) for the spatially flat DGP model with (without) SN systematic errors. The consistence of growth function data points is checked in terms of a relative departure of redshift-distance relation.
124921771
Search for neutral Higgs boson production through the process e+ e- --> Z* H0
Abstract The results of the searches for neutral Higgs boson production in the process e + e − → Z ∗ H 0 are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z 0 decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L. These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e + e − → Z ∗ h 0 are set. A lower limit of 66.7 GeV at 95% C.L. is obtained for the case where the Higgs decays into an invisible final state.
119228702
Cosmological evolution of the Fanaroff–Riley type II source population
By combining a model for the evolution of the radio luminosity of an individual source with the radio luminosity function, we perform a multidimensional Monte Carlo simulation to investigate the cosmological evolution of the Fanaroff–Riley type II (FR II) radio galaxy population by generating large artificial samples. The properties of FR II sources are required to evolve with redshift in the artificial samples to fit the observations. Either the maximum jet age or the maximum density of the jet environment or both evolve with redshift. We also study the distribution of FR II source properties as a function of redshift. From currently available data we cannot constrain the shape of the distribution of environment density or age, but jet power is found to follow a power-law distribution with an exponent of approximately −2. This power-law slope does not change with redshift out to z = 0.6. We also find the distribution of the pressure in the lobes of FR II sources to evolve with redshift up to z ∼ 1.2.
121882392
First results on the Spaghetti Calorimeter projective prototype
Abstract The performances of a projective lead/scintillating fibres (“spaghetti”) calorimeter made out of rectangular cross-section (32 × 32 mm 2 ) straight modules alternated with tapering modules at 2.5° are described. Beam test results on energy resolution, constant term suppression, lineshape, uniformity of response, shower position resolution, and electron-pion discrimination are presented. The readout of the fibres in the straight modules, which are sensitive to most of the electromagnetic showers and to part of the hadronic showers, is kept separate from the readout of the fibres of the wedged sections, which are sensitive only to hadronic showers. The lead-to-fibre volume ratio is kept at about 4 to 1 in order to obtain an equal-amplitude response from electrons and hadrons (usually called “compensation”). The origin of the energy resolution constant term has been better understood. This allowed the reduction of the constant term to 0.5%, down from 1.2% measured in older prototypes. The probability of faking abnormally large signals because of channelling effects is also discussed. The position resolution has been measured to range from 0.5 to 1 mm depending on the hit position of the particle. A comparison with the larger hexagonal module design is also made. The efficiency of a hardware thresholding of the wedges' signal as a level one trigger pion veto is discussed along with off-line electron/pion discrimination performances. Since the wedges start at 26 X 0 from the calorimeter front face they should show no signal for electromagnetic showers. It was found that electromagnetic showers of 50 GeV generate wedge signals of a maximum of a few tens of MeV. It was also found that the discriminating power is angle dependent, mainly because at small particle-to-fibre angles (≤ 1°) some electrons can penetrate the calorimeter through channeling, thus exciting a signal in the wedges. At slightly higher tilt angle it is possible to use a lower wedge threshold without loss in electron efficiency. With a beam-to-fibre angle of 3°, 99.6% of pions are rejected with a 98.5% electron efficiency. More recent and preliminary results on energy resolution at energies up to 100 GeV, and on radiation damage of scintillating fibres are also presented.
209869998
Observation of the decay psi(2S) ---> K*(892)anti-K + c.c.