119629909
Is modified gravity required by observations? An empirical consistency test of dark energy models
We apply the technique of parameter splitting to existing cosmological data sets, to check for a generic failure of dark energy models. Given a dark energy parameter, such as the energy density {omega}{sub {lambda}} or equation of state w, we split it into two meta-parameters with one controlling geometrical distances, and the other controlling the growth of structure. Observational data spanning Type Ia Supernovae, the cosmic microwave background (CMB), galaxy clustering, and weak gravitational lensing statistics are fit without requiring the two meta-parameters to be equal. This technique checks for inconsistency between different data sets, as well as for internal inconsistency within any one data set (e.g., CMB or lensing statistics) that is sensitive to both geometry and growth. We find that the cosmological constant model is consistent with current data. Theories of modified gravity generally predict a relation between growth and geometry that is different from that of general relativity. Parameter splitting can be viewed as a crude way to parametrize the space of such theories. Our analysis of current data already appears to put sharp limits on these theories: assuming a flat universe, current data constrain the difference {delta}{omega}{sub {lambda}}={omega}{sub {lambda}}(geom)-{omega}{sub {lambda}}(grow) to be -0.0044{sub -0.0057-0.0119}{sup +0.0058+0.0108} (68%more » and 95% C.L. respectively); allowing the equation of state w to vary, the difference {delta}w=w(geom)-w(grow) is constrained to be 0.37{sub -0.36-0.53}{sup +0.37+1.09}. Interestingly, the region w(grow)>w(geom), which should be generically favored by theories that slow structure formation relative to general relativity, is quite restricted by data already. We find w(grow)<-0.80 at 2{sigma}. As an example, the best-fit flat Dvali-Gabadadze-Porrati model approximated by our parametrization lies beyond the 3{sigma} contour for constraints from all the data sets.« less
119228934
Cosmological information in weak lensing peaks
Recent studies have shown that the number counts of convergence peaks N(kappa) in weak lensing (WL) maps, expected from large forthcoming surveys, can be a useful probe of cosmology. We follow up on this finding, and use a suite of WL convergence maps, obtained from ray-tracing N-body simulations, to study (i) the physical origin of WL peaks with different heights, and (ii) whether the peaks contain information beyond the convergence power spectrum P_ell. In agreement with earlier work, we find that high peaks (with amplitudes >~ 3.5 sigma, where sigma is the r.m.s. of the convergence kappa) are typically dominated by a single massive halo. In contrast, medium-height peaks (~0.5-1.5 sigma) cannot be attributed to a single collapsed dark matter halo, and are instead created by the projection of multiple (typically, 4-8) halos along the line of sight, and by random galaxy shape noise. Nevertheless, these peaks dominate the sensitivity to the cosmological parameters w, sigma_8, and Omega_m. We find that the peak height distribution and its dependence on cosmology differ significantly from predictions in a Gaussian random field. We directly compute the marginalized errors on w, sigma_8, and Omega_m from the N(kappa) + P_ell combination, including redshift tomography with source galaxies at z_s=1 and z_s=2. We find that the N(kappa) + P_ell combination has approximately twice the cosmological sensitivity compared to P_ell alone. These results demonstrate that N(kappa) contains non-Gaussian information complementary to the power spectrum.
18834437
Challenges to the DGP model from horizon-scale growth and geometry
We conduct a Markov Chain Monte Carlo study of the Dvali-Gabadadze-Porrati (DGP) selfaccelerating braneworld scenario given the cosmic microwave background (CMB) anisotropy, supernovae and Hubble constant data by implementing an effective dark energy prescription for modified gravity into a standard Einstein-Boltzmann code. We find no way to alleviate the tension between distance measures and horizon scale growth in this model. Growth alterations due to perturbations propagating into the bulk appear as excess CMB anisotropy at the lowest multipoles. In a flat
119405677
Constraining the evolution of dark energy with a combination of galaxy cluster observables
We show that the abundance and redshift distribution (dN/dz) of galaxy clusters in future high-yield cluster surveys, combined with the spatial power spectrum [P{sub c}(k)] of the same clusters, can place significant constraints on the evolution of the dark energy equation of state, w=w(a). We evaluate the expected errors on w{sub a}=-dw/da and other cosmological parameters using a Fisher matrix approach, and simultaneously including cluster structure evolution parameters in our analysis. We study three different types of forthcoming surveys that will identify clusters based on their x-ray emission (such as DUO, the Dark Universe Observatory), their Sunyaev-Zel'dovich (SZ) decrement (such as SPT, the South Pole Telescope), or their weak-lensing shear (such as LSST, the Large Synoptic Survey Telescope). We find that combining the cluster abundance and power spectrum significantly enhances constraints from either method alone. We show that the weak-lensing survey can deliver a constraint as tight as {delta}w{sub a}{approx}0.1 on the evolution of the dark energy equation of state, and that the x-ray and SZ surveys each yield {delta}w{sub a}{approx}0.4 separately, or {delta}w{sub a}{approx}0.2 when these two surveys are combined. For the x-ray and SZ surveys, constraints on dark energy parameters are improved by a factor of 2 bymore » combining the cluster data with cosmic microwave background anisotropy measurements by Planck, but degrade by a factor of 2 if the survey is required to solve simultaneously for cosmological and cluster structure evolution parameters. The constraint on w{sub a} from the weak-lensing survey is improved by {approx}25% with the addition of Planck data.« less
118485729
Chirality in odd-A Rh isotopes within the triaxial particle rotor model
By adopting the fully quantal triaxial particle-rotor model, the candidate chiral doublet bands in odd-A nuclei {sup 103}Rh and {sup 105}Rh with {pi}g{sub 9/2}{sup -1} x {nu}h{sub 11/2}{sup 2} configuration are studied. For the doublet bands in both nuclei, agreement is excellent for the observed energies over the entire spin range and B(M1)/B(E2) at higher spin range. The evolution of the chiral geometry with angular momentum is discussed in detail by using the angular momentum components and their probability distributions. Chirality is found to change from chiral vibration to nearly static chirality at spin I=37/2 and back to another type of chiral vibration at higher spin. The influence of the triaxial deformation {gamma} is also studied.
119212120
GENERALIZED HOLOGRAPHIC DARK ENERGY AND ITS OBSERVATIONAL CONSTRAINTS
In the original holographic dark energy (HDE) model, the dark energy density is proposed to be rho(de) = 3c(2)M(P)(2)L(-2), with c a dimensionless constant characterizing the properties of the HDE. In this work, we propose the generalized holographic dark energy (GHDE) model by considering the parameter c as a redshift-dependent function c(z). We derive all the physical quantities of the GHDE model analytically, and fit the c(z) by trying four kinds of parametrizations. The cosmological constraints of the c(z) are obtained from the joint analysis of the present SNLS3+BAO+CMB+H-0 data. We find that, compared with the original HDE model, the GHDE models can provide a better fit to the data. For example, the GHDE model with JBP-type c(z) can reduce the chi(2)(min) of the HDE model by 2.16. We also find that, unlike the original HDE model with a phantom-like behavior in the future, the GHDE models can present many more different possibilities, i.e. it allows the GHDE in the future to be either quintessence-like, cosmological constant-like, or phantom-like, depending on the forms of c(z).
209856078
Measurement of the Matrix Element for the Decay $\eta^{\prime} \to \eta \pi^+\pi^-$
7502694
Measurement of the top-quark mass in the lepton+jets channel using a matrix element technique with the CDF II detector
A measurement of the top-quark mass is presented using Tevatron data from proton-antiproton collisions at center-of-mass energy {radical}(s)=1.96 TeV collected with the CDF II detector. Events are selected from a sample of candidates for production of tt pairs that decay into the lepton+jets channel. The top-quark mass is measured with an unbinned maximum likelihood method where the event probability density functions are calculated using signal and background matrix elements, as well as a set of parametrized jet-to-parton transfer functions. The likelihood function is maximized with respect to the top-quark mass, the signal fraction in the sample, and a correction to the jet energy scale (JES) calibration of the calorimeter jets. The simultaneous measurement of the JES correction ({Delta}{sub JES}) amounts to an additional in situ jet energy calibration based on the known mass of the hadronically decaying W boson. Using the data sample of 578 lepton+jets candidate events, corresponding to 3.2 fb{sup -1} of integrated luminosity, the top-quark mass is measured to be m{sub t}=172.4{+-}1.4(stat+{Delta}{sub JES}){+-}1.3(syst) GeV/c{sup 2}.
118416982
Testing modified gravity models with recent cosmological observations
We explore the cosmological implications of five modified gravity (MG) models by using the recent cosmological observational data, including the recently released SNLS3 type Ia supernovae sample, the cosmic microwave background anisotropy data from the Wilkinson Microwave Anisotropy Probe 7-yr observations, the baryon acoustic oscillation results from the Sloan Digital Sky Survey data release 7, and the latest Hubble constant measurement utilizing the Wide Field Camera 3 on the Hubble Space Telescope. The MG models considered include the Dvali-Gabadadze-Porrati (DGP) model, two f (R) models, and two f (T) models. We find that compared with the ΛCDM model, MG models can not lead to an appreciable reduction of the χmin2. The analysis of AIC and BIC shows that the simplest cosmological constant model (ΛCDM) is still the most preferred by the current data, and the DGP model is strongly disfavored. In addition, from the observational constraints, we also reconstruct the evolutions of the growth factor in these models. We find that the current available growth factor data are not enough to distinguish these MG models from the ΛCDM model.