118465763
Current observational constraints to the holographic dark energy model with a new infrared cutoff via the Markov chain Monte Carlo method
In this paper, the holographic dark energy models with the new infrared cutoff for both the flat case and the nonflat case are confronted with the combined constraints of current cosmological observations: type Ia supernovae, baryon acoustic oscillations, current cosmic microwave background, and the observational Hubble data. By utilizing the Markov chain Monte Carlo method, we obtain the best fit values of the parameters with $1\ensuremath{\sigma}$, $2\ensuremath{\sigma}$ errors in the flat model: ${\ensuremath{\Omega}}_{b}{h}^{2}={0.0233}_{\ensuremath{-}0.0009\ensuremath{-}0.0014}^{+0.0009+0.0013}$, $\ensuremath{\alpha}={0.8502}_{\ensuremath{-}0.0875\ensuremath{-}0.1064}^{+0.0984+0.1299}$, $\ensuremath{\beta}={0.4817}_{\ensuremath{-}0.0773\ensuremath{-}0.0955}^{+0.0842+0.1176}$, ${\ensuremath{\Omega}}_{\mathrm{de}0}={0.7287}_{\ensuremath{-}0.0294\ensuremath{-}0.0429}^{+0.0296+0.0432}$, ${\ensuremath{\Omega}}_{m0}={0.2713}_{\ensuremath{-}0.0296\ensuremath{-}0.0432}^{+0.0294+0.0429}$, ${H}_{0}={66.35}_{\ensuremath{-}2.14\ensuremath{-}3.07}^{+2.38+3.35}$. In the nonflat model, the constraint results are found in $1\ensuremath{\sigma}$, $2\ensuremath{\sigma}$ regions: ${\ensuremath{\Omega}}_{b}{h}^{2}={0.0228}_{\ensuremath{-}0.0010\ensuremath{-}0.0014}^{+0.0010+0.0014}$, ${\ensuremath{\Omega}}_{k}={0.0305}_{\ensuremath{-}0.0134\ensuremath{-}0.0176}^{+0.0092+0.0140}$, $\ensuremath{\alpha}={0.8824}_{\ensuremath{-}0.1163\ensuremath{-}0.1378}^{+0.2180+0.2213}$, $\ensuremath{\beta}={0.5016}_{\ensuremath{-}0.0871\ensuremath{-}0.1102}^{+0.0973+0.1247}$, ${\ensuremath{\Omega}}_{\mathrm{de}0}={0.6934}_{\ensuremath{-}0.0304\ensuremath{-}0.0413}^{+0.0364+0.0495}$, ${\ensuremath{\Omega}}_{m0}={0.2762}_{\ensuremath{-}0.0302\ensuremath{-}0.0412}^{+0.0278+0.0402}$, ${H}_{0}={70.20}_{\ensuremath{-}3.17\ensuremath{-}4.00}^{+3.03+3.58}$. In the best fit holographic dark energy models, the equation of state of dark energy and the deceleration parameter at present are characterized by ${w}_{\mathrm{de}0}=\ensuremath{-}1.1414\ifmmode\pm\else\textpm\fi{}0.0608$, ${q}_{0}=\ensuremath{-}0.7476\ifmmode\pm\else\textpm\fi{}0.0466$ (flat case) and ${w}_{\mathrm{de}0}=\ensuremath{-}1.0653\ifmmode\pm\else\textpm\fi{}0.0661$, ${q}_{0}=\ensuremath{-}0.6231\ifmmode\pm\else\textpm\fi{}0.0569$ (nonflat case). Compared to the $\ensuremath{\Lambda}\mathrm{CDM}$ model, it is found the current combined data sets do not favor the holographic dark energy model over the $\ensuremath{\Lambda}\mathrm{CDM}$ model.
119217496
Revisiting generalized Chaplygin gas as a unified dark matter and dark energy model
In this paper, we revisit the generalized Chaplygin gas (GCG) model as a unified dark matter and dark energy model. The energy density of GCG model is given as ρGCG/ρGCG0=[Bs+(1−Bs)a−3(1+α)]1/(1+α), where α and Bs are two model parameters which will be constrained by type Ia supernova as standard candles, baryon acoustic oscillation as standard rulers and the seventh year full WMAP data points. In this paper, we will not separate GCG into dark matter and dark energy parts any more as adopted in the literature. By using the Markov Chain Monte Carlo method, we find the results $\alpha=0.00126_{-0.00126- 0.00126}^{+ 0.000970+ 0.00268}$ and $B_{s}= 0.775_{-0.0161- 0.0338}^{+ 0.0161+ 0.0307}$.
210001134
Reconstructing dark energy potentials from parameterized deceleration parameters
In this paper, the properties of dark energy are investigated according to the parameterized deceleration parameter q(z), which is used to describe the extent of the accelerating expansion of the universe. The potential of dark energy V() and the cosmological parameters, such as the dimensionless energy density ωo, Ωm, and the state parameter w, are connected to it. Concretely, by giving two kinds of parameterized deceleration parameters q(z) = a + bz/(1 + z) and q(z) = 1/2 + (az + b)/(1 + z)2, the evolution of these parameters and the reconstructed potentials V() are plotted and analysed. It is found that the potentials run away with the evolution of universe.
122268272
HIERARCHY IN HOŘAVA-LIKE GRAVITY
We investigate a Hořava-like gravity model in (4+1)-dimensional space–time. Differing from the original one, we put a critical exponent z to the extra space dimension, which preserves the 4-dimensional diffeomorphism. Surprisingly, we obtain a mass hierarchy in a way completely different from the Randall–Sundrum model, we also obtain an exponential factor solution with the use of Ricci-like flow. More interesting relations with AdS5/CFT4 are further demonstrated. Since AdS/CFT is a realization of holography, we conclude that the Hořava-like gravity may be also a realization of holography.
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.
119301936
Integrated Sachs-Wolfe effect in time varying vacuum model
The integrated Sachs-Wolfe (ISW) effect is an important implication for dark energy. In this paper, we have calculated the power spectrum of the ISW effect in the time varying vacuum cosmological model, where the model parameter $\ensuremath{\beta}=4.407$ is obtained by the observational constraint of the growth rate. It is found that the source of the ISW effect is not only affected by the different evolutions of the Hubble function $H(a)$ and the dimensionless matter density ${\ensuremath{\Omega}}_{m}(a)$, but also by the different growth function ${D}_{+}(a)$, all of which are changed due to the presence of a matter production term in the time varying vacuum model. However, the difference of the ISW effect in the $\ensuremath{\Lambda}(t)\mathrm{CDM}$ model and the $\ensuremath{\Lambda}\mathrm{CDM}$ model is lessened to a certain extent because of the integration from the time of last scattering to the present. It is implied that the observations of the galaxies with high redshift are required to distinguish the two models.
122632213
Calculation of muon final-state probabilities after muon-induced fission
Abstract Experiments have shown that in muonic uranium-238 fission the μ − is bound mainly to the heavy fragment with a few percent of cases of binding to the light fragment. We use time-dependent perturbation theory to calculate the theoretical branching for a variety of fission asymmetries and fission fragment dynamical conditions. We go beyond earlier theoretical works in that we study extended nuclear charge distributions as well as point charges. Agreement with experiment is within the limits of error.
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.
15082169
Search for Neutral Charmless B-Decays at Lep
Abstract A search for rare charmless decays of B d 0 and B s 0 mesons has been performed in the exclusive channels B d(s) 0 → ηη , B d(s) 0 → ηπ 0 and B d(s) 0 → π 0 π 0 . The data sample consisted of three million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1994. No candidate event has been observed and the following upper limits at 90% confidence level on the branching ratios have been set: Br ( B () d → ηη ) x 10 −4 , Br ( B () s → ηη ) x 10 −3 , Br ( B () d → ηφ () ) x 10 −4 , Br ( B () s → ηphi ; () ) x 10 −3 , Br ( B () d → phi ; () phi ; () ) x 10 −5 , Br ( B () s → phi ; () phi ; () ) x 10 −4 . These are the first experimental limits on B d 0 →ηη and on the B s 0 neutral charmless modes.
14009273
Measuring Time Dependence of Dark Energy Density from Type Ia Supernova Data
Observations of high-redshift supernovae imply an accelerating universe that can only be explained by an unusual energy component such as vacuum energy or quintessence. To assess the ability of current and future supernova data to constrain the properties of the dark energy, we allow its density to have arbitrary time dependence, ρX(z). This leads to an equation of state for the dark energy, wX(z) = pX(z)/ρX(z), which is a free function of redshift z. We find that current data of type Ia supernovae (SNe Ia) are consistent with a cosmological constant, with large uncertainties at z 0.5. We show that ρX(z)/ρX(z = 0) can be measured reasonably well to about z = 1.5 using SN Ia data from realistic future SN Ia pencil beam surveys, provided that the weak energy condition (energy density of matter is nonnegative for any observer) is imposed. While it is only possible to differentiate between different models (say, quintessence and k-essence) at z 1.5 using realistic data, the correct trend in the time dependence of the dark energy density can be clearly detected out to z = 2, even in the presence of plausible systematic effects. This would allow us to determine whether the dark energy is a cosmological constant or some exotic form of energy with a time-dependent density.
11259901
Present and future evidence for evolving dark energy
We compute the Bayesian evidences for one- and two-parameter models of evolving dark energy, and compare them to the evidence for a cosmological constant, using current data from Type Ia supernova, baryon acoustic oscillations, and the cosmic microwave background. We use only distance information, ignoring dark energy perturbations. We find that, under various priors on the dark energy parameters, LambdaCDM is currently favoured as compared to the dark energy models. We consider the parameter constraints that arise under Bayesian model averaging, and discuss the implication of our results for future dark energy projects seeking to detect dark energy evolution. The model selection approach complements and extends the figure-of-merit approach of the Dark Energy Task Force in assessing future experiments, and suggests a significantly-modified interpretation of that statistic.