16358983
Unbiased Estimate of Dark Energy Density from Type Ia Supernova Data
Type Ia supernovae (SNe Ia) are currently the best probes of the dark energy in the universe. To constrain the nature of dark energy, we assume a flat universe and that the weak energy condition is satisfied, and we allow the density of dark energy, ρX(z), to be an arbitrary function of redshift. Using simulated data from a space-based SN pencil-beam survey, we find that by optimizing the number of parameters used to parameterize the dimensionless dark energy density, f(z) = ρX(z)/ρX(z = 0), we can obtain an unbiased estimate of both f(z) and the fractional matter density of the universe, Ωm. A plausible SN pencil-beam survey (with a square degree field of view and for an observational duration of 1 yr) can yield about 2000 SNe Ia with 0 ≤ z ≤ 2. Such a survey in space would yield SN peak luminosities with a combined intrinsic and observational dispersion of σ(mint) = 0.16 mag. We find that for such an idealized survey, Ωm can be measured to 10% accuracy, and the dark energy density can be estimated to ~20% to z ~ 1.5, and ~20%-40% to z ~ 2, depending on the time dependence of the true dark energy density. Dark energy densities that vary more slowly can be more accurately measured. For the anticipated Supernova/Acceleration Probe (SNAP) mission, Ωm can be measured to 14% accuracy, and the dark energy density can be estimated to ~20% to z ~ 1.2. Our results suggest that SNAP may gain much sensitivity to the time dependence of the dark energy density and Ωm by devoting more observational time to the central pencil-beam fields to obtain more SNe Ia at z > 1.2. We use both a maximum likelihood analysis and a Monte Carlo analysis (when appropriate) to determine the errors of estimated parameters. We find that the Monte Carlo analysis gives a more accurate estimate of the dark energy density than the maximum likelihood analysis.
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.
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.
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.
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.
124790807
ILC 3.2 km damping ring design based on the FODO cell
We report on a new design for an ILC 3.2 km damping ring, with 2 arcs based on the FODO cell and 2 straight sections that are nearly the same as the newest version of the 6.4 km ring DCO4. This new lattice requires fewer magnets and a lower RF voltage, and has a better dynamic aperture than DCO4 while maintaining flexibility in regard to the momentum compaction factor. So far, this design is the only one satisfying all the requirements for a 3.2 km ring. The work on the lattice design and the dynamic aperture study is presented in detail.
119727400
A conformally broken system as the constrained SL(2,R) WZNW model, its integrability and dressing symmetry
This paper is devoted to the study of the conformally broken system related to the conformally invariant SL(2,R) WZNW model. Our starting point is such an action that is similar in form to the action of gauged WZNW theories developed by Balog et al. (1990). However, the Lagrangian multipliers in our case are assumed to take their values on the mixing of upper and lower Borel subalgebras of sl(2). The system obtained turns out to be an off-conformal extension of the sinh-Gordon model. Its integrability is displayed by the Lax formalism with an arbitrary spectral parameter, the classical r-matrix, and the hidden dressing symmetry.
119188783
Probing interaction and spatial curvature in the holographic dark energy model
In this paper we place observational constraints on the interaction and spatial curvature in the holographic dark energy model. We consider three kinds of phenomenological interactions between holographic dark energy and matter, i.e., the interaction term Q is proportional to the energy densities of dark energy (rho(A)), matter (p(m)), and matter plus dark energy (p(m) + p(A)). For probing the interaction and spatial curvature in the holographic dark energy model, we use the latest observational data including the type la supernovae (SNIa) Constitution data, the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement, from the Sloan Digital Sky Survey (SDSS). Our results show that, the interaction and spatial curvature in the holographic dark energy model are both rather small. Besides, it is interesting to find that there exists significant degeneracy between the phenomenological interaction and the spatial curvature in the holographic dark energy model.
119242452
Unified dark fluid with constant adiabatic sound speed and cosmic constraints
As is known above 90% of the energy content in Universe is made of unknown dark component. Usually this dark fluid is separated into two parts: dark matter and dark energy. However, it may be a mixture of these two energy components, or just one exotic unknown fluid. This property is dubbed as dark degeneracy. With this motivation, in this paper, a unified dark fluid having constant adiabatic sound speed $c_s^2=\alpha$, which is in the range $[0,1]$, is studied. At first, via the energy conservation equation, its energy density, $\rho_d/\rho_{d0}=(1-B_s)+B_s a^{-3(1+\alpha)}$ where $B_s$ is related to integration constant from energy conservation equation as another model parameter, is presented. Then by using Markov Chain Monte Carlo method with currently available cosmic observational data sets which include type Ia supernova Union 2, baryon acoustic oscillation and WMAP 7-year data of cosmic background radiation, we show that small values of $\alpha$ are favored in this unified dark fluid model. Furthermore, we show that smaller values of $\alpha<10^{-5}$ are required to match matter (baryon) power spectrum from SDSS DR7.
119263928
Made-to-measure galaxy models – III. Modelling with Milky Way observations
We demonstrate how the Syer and Tremaine made-to-measure method of stellar dynamical modelling can be adapted to model a rotating galactic bar. We validate our made-to-measure changes using observations constructed from the existing Shen et al. N-body model of the Milky Way bar, together with kinematic observations of the Milky Way bulge and bar taken by the Bulge Radial Velocity Assay. Our results for a combined determination of the bar angle and bar pattern speed (approximate to 30 degrees and approximate to 40 km s(-1) kpc(-1)) are consistent with those determined by the N-body model. Whilst the made-to-measure techniques we have developed are applied using a particular N-body model and observational data set, they are in fact general and could be applied to other Milky Way modelling scenarios utilizing different N-body models and data sets. Additionally, we use the exercise as a vehicle for illustrating how N-body and made-to-measure methods might be combined into a more effective method.