119245573
Observational constraints on unified dark matter including Hubble parameter data
Abstract We constrain a unified dark matter (UDM) model from the latest observational data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state P X = p 0 + α ρ X . Our data set contains the newly revised H ( z ) data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: Ω Λ = 0.719 − 0.0305 + 0.0264 ( 1 σ ) − 0.0458 + 0.0380 ( 2 σ ) , α = 1.72 − 4.79 + 3.92 ( 1 σ ) − 7.30 + 5.47 ( 2 σ ) ( × 10 − 3 ) , Ω b h 2 = 0.0226 − 0.0011 + 0.0011 ( 1 σ ) − 0.0015 + 0.0016 ( 2 σ ) . Moreover, when considering a non-flat universe, Ω Λ = 0.722 − 0.0447 + 0.0362 ( 1 σ ) − 0.0634 + 0.0479 ( 2 σ ) , α = 0.242 − 0.775 + 0.787 ( 1 σ ) − 1.03 + 1.10 ( 2 σ ) ( × 10 − 2 ) , Ω b h 2 = 0.0227 − 0.0014 + 0.0015 ( 1 σ ) − 0.0018 + 0.0021 ( 2 σ ) , Ω k = − 0.194 − 1.85 + 2.02 ( 1 σ ) − 2.57 + 2.75 ( 2 σ ) ( × 10 − 2 ) . These give a more stringent results than before. We also give the results from other combinations of these data for comparison. The observational Hubble parameter data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the parameters α and Ω k are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.
118428312
Energy conditions and stability in generalized f(R) gravity with arbitrary coupling between matter and geometry
Abstract The energy conditions and the Dolgov–Kawasaki criterion in generalized f ( R ) gravity with arbitrary coupling between matter and geometry are derived in this Letter, which are quite general and can degenerate to the well-known energy conditions in GR and f ( R ) gravity with non-minimal coupling and non-coupling as special cases. In order to get some insight on the meaning of these energy conditions and the Dolgov–Kawasaki criterion, we apply them to a class of models in the FRW cosmology and give some corresponding results.
119262999
Extended Analysis on New Generalized Chaplygin Gas
We extend the study of the new generalized Chaplygin gas (NGCG) based on [J. Cosmol. Astropart. Phys. 0601 (2006) 003]. Specifically, we not only discuss the change rates of the energy densities and the energy transfer of this model, but also perform the Om diagnostic to differentiate the ΛCDM model from the NGCG and the GCG models. Furthermore, in order to consider the influence of dark energy on structure formation, we also present the evolution of the growth index in this scenario with interaction.
122901072
INTERACTING GENERALIZED CHAPLYGIN GAS MODEL WITH HOLOGRAPHIC DARK ENERGY
In this paper we consider the interacting generalized Chaplygin gas model as a unified scheme, in which the holographic dark energy as the dark energy component interacts with the cold dark matter with wdm = 0. Concretely, we mainly discuss the two kinds of interactions between the dark energy and dark matter, and give the evolution trajectories of density parameter and equation of state of dark energy as well as the decelerate parameter. By analysis, we show that in both cases of Q = 3bHρde and Q = 3bHρGCG, the evolution laws and the present values of Ωde, wde and q are compatible with the astronomical observations, but the effects of the coupling constant and holographic constant on them are completely different.
118610495
Conditions and instability in f(R) gravity with non-minimal coupling between matter and geometry
In this paper, on the basis of the generalized f(R) gravity model with arbitrary coupling between geometry and matter, four classes of f(R) gravity models with non-minimal coupling between geometry and matter will be studied. By means of conditions of power-law expansion and the equation of state of matter less than −1/3, the relationship among p, w and n, the conditions and the candidate for late-time cosmic accelerated expansion will be discussed in the four classes of f(R) gravity models with non-minimal coupling. Furthermore, in order to keep to considering models that are realistic ones, the Dolgov–Kawasaki instability will be investigated in each of them.
15774561
The dependence of galaxy formation on cosmological parameters: can we distinguish between the WMAP1 and WMAP3 parameter sets?
We combine N-body simulations of structure growth with physical modelling of galaxy evolution to investigate whether the shift in cosmological parameters between the first- and third-year results from the Wilkinson Microwave Anisotropy Probe (WMAP) affects predictions for the galaxy population. Structure formation is significantly delayed in the WMAP3 cosmology, because the initial matter fluctuation amplitude is lower on the relevant scales. The decrease in dark matter clustering strength is, however, almost entirely offset by an increase in halo bias, so predictions for galaxy clustering are barely altered. In both cosmologies, several combinations of physical parameters can reproduce observed, low-redshift galaxy properties; the star formation, supernova feedback and active galactic nucleus feedback efficiencies can be played off against each other to give similar results. Models which fit observed luminosity functions predict projected two-point correlation functions which scatter by about 10-20 per cent on large scale and by larger factors on small scale, depending both on cosmology and on details of galaxy formation. Measurements of the pairwise velocity distribution prefer the WMAP1 cosmology, but careful treatment of the systematics is needed. Given present modelling uncertainties, it is not easy to distinguish between the WMAP] and WMAP3 cosmologies on the basis of low-redshift galaxy properties. Model predictions diverge more dramatically at high redshift. Better observational data at z > 2 will better constrain galaxy formation and perhaps also cosmological parameters.
119162725
Observation of CP violation in B+ to DK+ decays
An analysis of B → DK and B → Dπ decays is presented where the D meson is reconstructed in the two-body final states: Kπ, KK, ππ and πK. Using 1.0 fb of LHCb data, measurements of several observables are made including the first observation of the suppressed mode B ± → [πK]DK . CP violation in B → DK decays is observed with 5.8σ significance. Submitted to Physics Letters B
11144784
A Chandra Study of the Rosette Star-forming Complex. I. The Stellar Population and Structure of the Young Open Cluster NGC 2244
We present the first high spatial resolution X-ray study of NGC 2244, the 2 Myr old stellar cluster in the Rosette Nebula, using Chandra. Over 900 X-ray sources are detected; 77% have optical or FLAMINGOS NIR stellar counterparts and are mostly previously uncataloged young cluster members. The X-ray-selected population is estimated to be nearly complete between 0.5 and 3 M☉. A number of further results emerge from our analysis: (1) The X-ray LF and the associated K-band LF indicate a normal Salpeter IMF for NGC 2244. This is inconsistent with the top-heavy IMF reported from earlier optical studies that lacked a good census of log (LX/Lbol) ~ − 7 relation. The Rosette OB X-ray spectra are soft and consistent with the standard model of small-scale shocks in the inner wind of a single massive star.
12993780
Measurement of CC interactions produced by ${}^8$B solar neutrinos at SNO
122330531
Search for dark matter and large extra dimensions in monojet events in pp collisions at $ \sqrt {s} = {7} $ TeV
A bstractA search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter MD determined as a function of the number of extra dimensions are also an improvement over the previous results.