Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes

We use recent data: the 192 ESSENCE type Ia supernovae (SNe Ia), the 182 Gold SNe Ia, the three-year WMAP, the SDSS baryon acoustic peak, the X-ray gas mass fraction in clusters and the observational H(z) data, to constrain models of the accelerating universe. Combining the 192 ESSENCE data with the observational H(z) data to constrain the parameterized deceleration parameter, we obtain the best-fit values of the transition redshift and current deceleration parameter z _T=0.632_−0.127^+0.256 and q ₀=−0.788_−0.182^+0.182. Furthermore, using the ΛCDM model and two model-independent equations of state of the dark energy, we find that the combined constraint from the 192 ESSENCE data and four other cosmological observations gives smaller values for Ω _0m and q ₀, but a larger value for z _T than the combined constraint from the 182 Gold data with four other observations. Finally, according to the Akaike information criterion it is shown that the recently observed data equally support three dark energy models: ΛCDM, w _de(z)=w ₀ and w _de(z)=w ₀+w ₁ln (1+z).     

Running coupling: does the coupling between dark energy and dark matter change sign during the cosmological evolution?

In this paper we put forward a running coupling scenario for describing the interaction between dark energy and dark matter. The dark sector interaction in our scenario is free of the assumption that the interaction term Q is proportional to the Hubble expansion rate and the energy densities of dark sectors. We only use a time-variable coupling b(a) (with a the scale factor of the universe) to characterize the interaction Q. We propose a parametrization form for the running coupling b(a)=b ₀ a+b _e (1−a) in which the early-time coupling is given by a constant b _e , while today the coupling is given by another constant, b ₀. For investigating the feature of the running coupling, we employ three dark energy models, namely, the cosmological constant model (w=−1), the constant w model (w=w ₀), and the time-dependent w model (w(a)=w ₀+w ₁(1−a)). We constrain the models with the current observational data, including the type Ia supernova, the baryon acoustic oscillation, the cosmic microwave background, the Hubble expansion rate, and the X-ray gas mass fraction data. The fitting results indicate that a time-varying vacuum scenario is favored, in which the coupling b(z) crosses the noninteracting line (b=0) during the cosmological evolution and the sign changes from negative to positive. The crossing of the noninteracting line happens at around z=0.2–0.3, and the crossing behavior is favored at about 1σ confidence level. Our work implies that we should pay more attention to the time-varying vacuum model and seriously consider the phenomenological construction of a sign-changeable or oscillatory interaction between dark sectors.     

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 ρ _GCG/ρ _GCG0=[B _s +(1−B _s )a ^−3(1+α)]^1/(1+α), where α and B _s 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 a = 0.00126_{-0.00126- 0.00126}^{+ 0.000970+ 0.00268}\alpha=0.00126_{-0.00126- 0.00126}^{+ 0.000970+ 0.00268} and B_s = 0.775_{-0.0161- 0.0338}^{+ 0.0161+ 0.0307}B_{s}= 0.775_{-0.0161- 0.0338}^{+ 0.0161+ 0.0307}.     

Features of holographic dark energy under combined cosmological constraints

We investigate the observational signatures of the holographic dark-energy models, including both the original model and a model with an interaction term between the dark energy and dark matter. We first delineate the dynamical behavior of such models, especially considering whether they would have a “big rip” for different parameters; then we use several recent observations, including 182 high-quality type Ia supernovae data observed with the Hubble Space Telescope, the SNLS and ESSENCE surveys, 42 latest Chandra X-ray cluster gas mass fraction, 27 high-redshift gamma-ray burst samples, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, and the CMB shift parameter from the WMAP three-year result to give more reliable and tighter constraints on the holographic dark-energy models. The results of our constraints for the holographic dark-energy model without interaction is c=0.748_−0.009^+0.108, Ω _m0=0.276_−0.016^+0.017, and for the model with interaction (c=0.692_−0.107^+0.135, Ω _m0=0.281_−0.017^+0.017, α=−0.006_−0.024^+0.021, where α is an interacting parameter). As these models have more parameters than the ΛCDM model, we use the Bayesian Evidence as a model-selection criterion to make comparisons. We found that the holographic dark-energy models are mildly favored by the observations as compared to the ΛCDM model.     

Cosmological constraints on the generalized holographic dark energy

We use the Markov Chain Monte Carlo method to investigate global constraints on the generalized holographic (GH) dark energy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic dark energy can cross over the phantom boundary w _de =−1.     

The superconducting properties of YBa2(Cu1−xMx)3O7 for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa₂(Cu_1−xNi_x)₃O_7−y withx=0.1 and 0.2, and YBa₂(Cu_1−x Zn _x )₃O_7−y withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs⁻¹.1.6μs⁻¹, and 1 μs⁻¹ forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs⁻¹, 0.75 μs⁻¹, 0.65 μs⁻¹, and 0.4 μs⁻¹ forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.     

Interacting ghost dark energy in non-flat universe

A new dark energy model called “ghost dark energy” was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ _D  = α H, where α is a constant of order L_QCD³{\Lambda_{\rm QCD}^3} and Λ_QCD ~ 100 MeV is QCD mass scale. In this Letter, we extend the ghost dark energy model to the universe with spatial curvature in the presence of interaction between dark matter and dark energy. We study cosmological implications of this model in detail. In the absence of interaction the equation of state parameter of ghost dark energy is always w _D > −1 and mimics a cosmological constant in the late time, while it is possible to have w _D < −1 provided the interaction is taken into account. When k = 0, all previous results of ghost dark energy in flat universe are recovered. For the observational test, we use Supernova type Ia Gold sample, shift parameter of cosmic microwave background radiation and the correlation of acoustic oscillation on the last scattering surface and the baryonic acoustic peak from Sloan Digital Sky Survey are used to confine the value of free parameter of mentioned model.     

<Emphasis Type="Italic">Om</Emphasis> Diagnostic for Two-Parameter <Emphasis Type="Italic">ω</Emphasis><Subscript><Emphasis Type="Italic">σ</Emphasis></Subscript> in Dilaton Dark Energy

Om diagnostic is a good geometric method to differentiate one dark energy model from LCDM. We apply three different two-parameter equation of state ω _σ (EOS) to Dilaton Dark energy (DDE) model and investigate the Om diagnostic for these cases. We obtain that DDE model can be easily distinguished from LCDM no matter which case is considered. We also investigate the influence of coupled parameter α on the evolutive behavior of Om−z. According to the numerical result of Om, we get the current value of equation of state ω _σ0=−0.939 which fits the observational data well.     

One-dimensional ionic conduction in solid Ag2 Tl6I10

The ionic and electronic conductivities of Ag₂Tl₆I₁₀ single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag⁺-ion conductor parallel toc-direction, with the Ag⁺ ions moving through linear channels that are not interconnected. The conductivity σ_‖c =1.6×10⁻⁷Ω⁻¹cm⁻¹ at 25°C, with an activation enthalpy for σ_‖c of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ_⊥c =3×10⁻⁹Ω⁻¹cm⁻¹ at 25°C and an activation enthalpy for σ_⊥c of 0.64 eV. This is the first observation of one-dimensional Ag⁺ conduction and this type of orientation-dependent change from ionic to electronic conduction. On leave from Institute of Physics, Academia Sinica, Peking, China.     

The Moduli of Flat PGL(2,ℝ) Connections on¶Riemann Surfaces

Suppose X is a compact Riemann surface with genus g>1. Each class [σ] ∈ Hom(π₁(X),PGL(2,ℝ))/PGL(2,ℝ) is associated with the first and second Stiefel–Whitney classes w ₁([σ]) and w ₂([σ]). The set of representation classes with a fixed w ₁≠ 0 has two connected components. These two connected components are characterized by w ₂ being 0 or 1. For each fixed w ₁≠ 0, we prove that the component, characterized by w ₂= 0, contains an open dense set diffeomorphic to the total space of a vector bundle of rank 2g−2 over a once punctured algebraic torus of dimension g−1. The other component, characterized by w ₂= 1, contains an open dense set diffeomorphic to the total space of a vector bundle of rank 2g−2 over an algebraic torus of dimension g−1. Received: 2 January 1997 / Accepted: 28 November 1998     

Absence of Magnetism in Continuous-Spin Systems with Long-Range Antialigning Forces

We consider continuous-spin models on the d-dimensional hypercubic lattice with the spins σ _x a priori uniformly distributed over the unit sphere in ℝ ⁿ (with n≥2) and the interaction energy having two parts: a short-range part, represented by a potential Φ, and a long-range antiferromagnetic part λ|x−y|^−s σ _x ⋅σ _y for some exponent s>d and λ≥0. We assume that Φ is twice continuously differentiable, finite range and invariant under rigid rotations of all spins. For d≥1, s∈(d,d+2] and any λ>0, we then show that the expectation of each σ _x vanishes in all translation-invariant Gibbs states. In particular, the spontaneous magnetization is zero and block-spin averages vanish in all (translation invariant or not) Gibbs states. This contrasts the situation of λ=0 where the ferromagnetic nearest-neighbor systems in d≥3 exhibit strong magnetic order at sufficiently low temperatures. Our theorem extends an earlier result of A. van Enter ruling out magnetized states with uniformly positive two-point correlation functions.     

Finite-dimensional representations of a shock algebra

Abstruct The algebra describing a shock measure in the asymmetric simple exclusion model, seen from a second class particle, has finite-dimensional representations if and only if the asymmetry parameterp of the model and the left and right asymptotic densitiesp _± of the shock satisfy [(1−p)/p] ^r =p ₋(1−p ₊)/p ₊(1−p ₋) for some integerr≥1; the minimal dimension of the representation is then 2r. These representations can be used to calculate correlation functions in the model.     

Limits on decaying dark energy density models from the CMB temperature–redshift relation

The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (Phys Rev D 54:2571, 1996). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the cosmic microwave background (CMB) which depends on the effective equation of state w _eff and on the “adiabatic index” γ. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev–Zel’dovich observations and at higher redshift from quasar absorption line spectra, we find w _eff = −0.97 ± 0.03, adopting for the adiabatic index γ = 4/3, in good agreement with current estimates and still compatible with w _eff = −1, implying that the dark energy content being constant in time.     

Prospects for the measurement of the structure of the coupling of a Higgs boson to weak gauge bosons in weak boson fusion with the ATLAS detector

The prospects for the measurement of the tensor structure of the vertex between a standard model Higgs boson and two weak gauge bosons using the distribution of the azimuthal angles between the two tagging jets in the weak boson fusion channel are studied in a Monte Carlo analysis using the fast simulation of the ATLAS detector. The decay channels H→τ⁺τ^-→ll+4ν, H→τ⁺τ^-→lh+3ν at m_H=120 GeV and H→W⁺W^-→llνν at m_H=160 GeV are used in the analysis. For a standard model Higgs boson it is found that purely anomalous couplings are expected to be excluded at a confidence level corresponding to 2σ or more at m_H=120 GeV and more than 5σ at m_H=160 GeV from 30 fb^-1 of data. With a value of 1 roughly reproducing the standard model cross section for a purely anomalous coupling, the standard deviation in a measurement of a contribution of a CP even anomalous coupling in addition to the standard model coupling is estimated to be 0.20 at m_H=120 GeV and 0.09 at m_H=160 GeV.     

Bound on the Equation of State of Dark Energy from the Generalized Second Law of Thermodynamics

Assuming that the equation of state of dark energy is a constant, we obtain the allowed interval of the equation of state of dark energy: w _D≥−1, bounded from the generalized second law of thermodynamics, in a universe enveloped by the apparent horizon and containing a Schwarzschild black hole.     

Positron scattering from hydrocarbons

The total cross sections for positron impact on hydrocarbons have been calculated using the additivity rule in which the total cross section for a molecule is the sum of the total cross section for the constituent atoms. The energy range considered is from a few eV to several thousand eV. The total cross sections for positron impact on an atom are calculated by employing a complex spherical potential which comprises of a static, polarization and an absorption potential. We have good agreement with the experimental results for hydrocarbons for positron energy ⩾100 eV. Our results also agree with the available calculations for CH₄ and C₂H₂ which employed full molecular wavefunctions beyond 100 eV. Our absorption cross sections also agree with molecular wave-function calculations for C₂H₂ and CH₄ beyond 100 eV. We have shown the Bethe plots fore ⁺−C ande ⁺−H scattering systems and Bethe parameters have been extracted. We have fitted the cross section for positron impact on hydrocarbons in the formσ _t(C _n H _m )=naE ⁻ b+mcE ⁻ d in the energy range 300–5000 eV wherea=195.0543,b=0.7986,c=371.1757 andd=1.1379 withE in eV andσ _t in 10⁻¹⁶ cm².     

Superconductivity and magnetic ordering in YBa2(Cu1−x Fe x )3O7

Transverse-and zero-field μSR measurements have been made for YBa₂(Cu_1−x Fe _x )₃O₇ withx=0.04, 0.08 and 0.12. The temperature range studied was from approximately 7.5 K to 100 K. The onset of magnetic ordering commences at about 7.5 K forx=0.04, 10 K forx=0.08 and 20 K forx=0.12. The Gaussian depolarization parameter, σ ofG _x (t) = exp(−σ² t ²/2), is depressed by a factor of about 0.6 forx=0.04, but for thex=0.08 sample σ is depressed by a factor of 10 and increasing suppression is seen as the temperature is lowered below 45 K. This decrease in σ is interpreted in terms of decreasing electronic mean free paths.     

Non-steady-state photo-EMF in nanostructured GaN and polypyrrole within porous matrices

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=442 nm, I ₀=0.045–0.19 W/cm², T=293 K) and σ=(3.5–4.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=532 nm, I ₀=2.3 W/cm², T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L _D=0.18 μm.     

Statefinder Diagnostic and w?w′ Analysis for Interacting Polytropic Gas Dark Energy Model

The interacting polytropic gas dark energy model is investigated from the viewpoint of statefinder diagnostic tool and w−w′ analysis. The dependency of the statefinder parameters on the parameter of the model as well as the interaction parameter between dark matter and dark energy is calculated. We show that different values of the parameters of model and different values of interaction parameter result different evolutionary trajectories in s−r and w−w′ planes. The polytropic gas model of dark energy mimics the standard ΛCDM model at the early time.