118453039
Holographic dark energy in a universe with spatial curvature and massive neutrinos: a full Markov Chain Monte Carlo exploration
In this paper, we report the results of constraining the holographic dark energy model with spatial curvature and massive neutrinos, based on a Markov Chain Monte Carlo global fit technique. The cosmic observational data include the full WMAP 7-yr temperature and polarization data, the type Ia supernova data from Union2.1 sample, the baryon acoustic oscillation data from SDSS DR7 and WiggleZ Dark Energy Survey, and the latest measurements of H-0 from HST. To deal with the pertubations of dark energy, we adopt the parameterized post-Friedmann method. We find that, for the simplest holographic dark energy model without spatial curvature and massive neutrinos, the phenomenological parameter c < 1 at more than 4 sigma confidence level. The inclusion of spatial curvature enlarges the errors bars and leads to c < 1 only in about 2.5 sigma range; in contrast, the inclusion of massive neutrinos does not have significant influence on c. We also find that, for the holographic dark energy model with spatial curvature but without massive neutrinos, the 3 sigma errors bars of the current fractional curvature density Omega k(0) are still in order 10(-2); for the model with massive neutrinos but without spatial curvature, the 2 sigma upper bound of the total mass of neutrinos is Sigma m(v) < 0.48eV. Moreover, there exists clear degeneracy between spatial curvature and massive neutrinos in the holographic dark energy model, which enlarges the upper bound of Sigma m(v) by more than 2 times. In addition, we demonstrate that, making use of the full WMAP data can give better constraints on the holographic dark energy model, compared with the case using the WMAP "distance priors".
119224877
Cosmic Age Test in Inhomogeneous Cosmological Models Mimicking $\Lambda$CDM on the Light-Cone
The possibility of reconstructing a spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi (LTB) model with Lambda CDM observations has drawn much attention. Recently, an inhomogeneous LTB model having the same luminosity-distance and light-cone mass density of the homogeneous Lambda CDM model was reconstructed. From the Wilkinson microwave anisotropy probe 7-year measurements together with other cosmological observations, we calculate the cosmic age at our position in this LTB model, and obtain a constraint t(LTB) < 11.7 Gyr at 1 sigma confidence level. We find that this result is, although 2 Gyr younger compared with the age of the homogeneous Lambda CDM model, still within 1 sigma agreement with the constraint of cosmic age given by current astronomical measurements. We expect that in the future, with the help of more advanced observations, we can distinguish the reconstructed inhomogeneous LTB model from the homogeneous Lambda CDM model.
117232504
Revisit of Tension in Recent SNIa Datasets
Although today there are many observational methods, Type Ia supernovae (SNIa) is still one of the most powerful tools to probe the mysterious dark energy (DE). The most recent SNIa datasets are the 307 SNIa "Union" dataset \cite{kow08} and the 397 SNIa "Constitution" dataset \cite{hic09}. In a recent work \cite{wei10}, Wei pointed out that both Union and Constitution datasets are in tension with the observations of cosmic microwave background (CMB) and baryon acoustic oscillation (BAO), and suggested that two truncated versions of Union and Constitution datasets, namely "UnionT" and "ConstitutionT", should be used to constrain various DE models. But in \cite{wei10}, only the $\Lambda$CDM model is used to select the outliers from the Union and the Constitution dataset. In principle, since different DE models may select different outliers, the truncation procedure should be performed for each different DE model. In the present work, by performing the truncation procedure of \cite{wei10} for 10 different models, we demonstrate that the impact of different models is negligible, and the approach adopted in \cite{wei10} is valid. Moreover, by using the 4 SNIa datasets mentioned above, as well as the observations of CMB and BAO, we perform best-fit analysis on the 10 models. It is found that: (1) For each DE model, the truncated SNIa datasets not only greatly reduce $\chi_{min}^{2}$ and $\chi_{min}^{2}/dof$, but also remove the tension between SNIa data and other cosmological observations. (2) The CMB data is very helpful to break the degeneracy among different parameters, and plays a very important role in distinguishing different DE models. (3) The current observational data are still too limited to distinguish all DE models.
124269158
Thermodynamics of Schwarzschild de Sitter spacetimes: variable cosmological constant
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.
118441515
Dark energy: A brief review
The problem of dark energy is briefly reviewed in both theoretical and observational aspects. In the theoretical aspect, dark energy scenarios are classified into symmetry, anthropic principle, tuning mechanism, modified gravity, quantum cosmology, holographic principle, back-reaction and phenomenological types. In the observational aspect, we introduce cosmic probes, dark energy related projects, observational constraints on theoretical models and model independent reconstructions.
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
119640767
Measurement of the final states omega pi0, rho eta, and rho eta prime from psi (2S) electromagnetic decays and e+e- annihilations
Cross sections and form factors for $\ee \to \wpi$, $\rho\eta$, and $\rho\etap$ at center of mass energies of 3.650, 3.686, and 3.773 GeV are measured using data samples collected with the BESII detector at the BEPC. Also, the branching fractions of $\psi(2S) \rar \wpi$, $\rho\eta$, and $\rho\etap$ are determined to be $(1.87^{+0.68}_{-0.62}\pm0.28)\times 10^{-5}$, $(1.78^{+0.67}_{-0.62}\pm0.17)\times 10^{-5}$, and $(1.87^{+1.64}_{-1.11}\pm0.33)\times10^{-5}$, respectively.
119209325
Response of the Photospheric Magnetic Field to the X2.2 Flare on 2011 February 15
It is well known that the long-term evolution of the photospheric magnetic field plays an important role in building up free energy to power solar eruptions. Observations, despite being controversial, have also revealed a rapid and permanent variation of the photospheric magnetic field in response to the coronal magnetic field restructuring during the eruption. The Helioseismic and Magnetic Imager instrument (HMI) on board the newly launched Solar Dynamics Observatory produces seeing-free full-disk vector magnetograms at consistently high resolution and high cadence, which finally makes possible an unambiguous and comprehensive study of this important back-reaction process. In this study, we present a near disk-center, GOES-class X2.2 flare, which occurred in NOAA AR 11158 on 2011 February 15. Using the magnetic field measurements made by HMI, we obtained the first solid evidence of a rapid (in about 30 minutes) and irreversible enhancement in the horizontal magnetic field at the flaring magnetic polarity inversion line (PIL) by a magnitude of {approx}30%. It is also shown that the photospheric field becomes more sheared and more inclined. This field evolution is unequivocally associated with the flare occurrence in this sigmoidal active region, with the enhancement area located in between the two chromospheric flare ribbons andmore » the initial conjugate hard X-ray footpoints. These results strongly corroborate our previous conjecture that the photospheric magnetic field near the PIL must become more horizontal after eruptions, which could be related to the newly formed low-lying fields resulting from the tether-cutting reconnection.« less
109931583
The experimental study on beam-photoelectron instability in BEPC
A vertical coupled bunch instability explained as the photoelectron instability (PEI) was observed in the photon factory at KEK. To further investigate the instability, the experiments on the PEI have been carried out in Beijing Electron Positron Collider (BEPC) with the collaboration between MEP, China and KEK, Japan. Many interesting phenomena have been observed for different sets of parameters.
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