118575807
Model-Independent Distance Measurements from Gamma-Ray Bursts and Constraints on Dark Energy
Gamma-ray bursts (GRB) are the most energetic events in the Universe and provide a complementary probe of dark energy by allowing the measurement of cosmic expansion history that extends to redshifts greater than 6. Unlike type Ia supernovae (SNe Ia), GRBs must be calibrated for each cosmological model considered, because of the lack of a nearby sample of GRBs for model-independent calibration. For a flat universe with a cosmological constant, we find {omega}{sub m}=0.25{sub -0.11}{sup +0.12} from 69 GRBs alone. We show that the current GRB data can be summarized by a set of model-independent distance measurements, with negligible loss of information. We constrain a dark energy equation of state linear in the cosmic scale factor using these distance measurements from GRBs, together with the ''Union'' compilation of SNe Ia, WMAP five-year observations, and the SDSS (Sloan Digital Sky Survey) baryon acoustic oscillation scale measurement. We find that a cosmological constant is consistent with current data at 68% confidence level for a flat universe. Our results provide a simple and robust method to incorporate GRB data in a joint analysis of cosmological data to constrain dark energy.
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.
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.
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.
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.
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.
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.
56215933
PLC and Linux based control system for the CAMD Linac
Louisiana State University Center for Advanced Microstructures and Devices (CAMD) began operations in the fall of 1992. At the time, the facility had separate control systems for the storage ring and Linac. In 1997, CAMD began a control system upgrade project with the goal of producing a single unified control system running on the PC/Linux platform. After completion of the storage ring control system, the Linac control system was designed utilizing AutomationDirect.com PLCs for the real-time components, and PC/Linux for the user interface. The new Linac control system has been completed, and has been operational since July 2002. This paper will discuss the objectives, design, and future upgrade plans for the Linac control system, as well as the experiences with replacing the CGR-MeV VME/OS/9 control system with a PLC/PC/Linux based system.
118542607
Cosmological constraints on the generalized holographic dark energy
We use the Markov Chain Monte Carlo method to investigate global constraints on the generalized holographic (GH) dark energy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic dark energy can cross over the phantom boundary wde=−1.
118387621
Underground Prototype Water Cherenkov Muon Detector with the Tibet Air Shower Array
We are planning to build a 10,000 m2 water‐Cherenkov‐type muon detector (MD) array under the Tibet air shower (AS) array. The Tibet AS+MD array will have the sensitivity to detect gamma rays in the 100 TeV region by an order of the magnitude better than any other previous existing detectors in the world. In the late fall of 2007, a prototype water Cherenkov muon detector of approximately 100 m2 was constructed under the existing Tibet AS array. The preliminary data analysis is in good agreement with our MC simulation. We are now ready for further expanding the underground water Cherenkov muon detector.
16629143
K/pi Fluctuations at relativistic energies.
We report K/pi fluctuations from Au + Au collisions at sqrt[s(NN)]= 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. K/pi fluctuations in central collisions show little dependence on incident energy and are on the same order as those from NA49 at the Super Proton Synchrotron in central Pb + Pb collisions at sqrt[s(NN)]=12.3 and 17.3 GeV. We report results for the collision centrality dependence of K/pi fluctuations and results for charge-separated fluctuations. We observe that the K/pi fluctuations scale with the charged particle multiplicity density.