122814293
Constraints on generalized Chaplygin gas model including gamma-ray bursts
Generalized Chaplygin gas (whose equation of state is p GCG = − A/ρ α G CG ) was proposed as a candidate for uni fi cation of dark energy and dark matter. We investigate constraints on this model with the latest observed data. We test the model with type-Ia supernovae (SNe Ia), cosmic microwave background (CMB) anisotropy, X-ray gas mass fractions in clusters, and gamma-ray bursts (GRBs). We calibrate the GRB luminosity relations without assuming any cosmological models using SNe Ia. We show that GRBs can extend the Hubble diagram to higher redshifts ( z > 6 ). The GRB Hubble diagram is well behaved and delineates the shape of the Hubble diagram well. We measure A s ≡ A /ρ α +1 GCG , 0 = 0 . 68 +0 . 04 − 0 . 08 (where ρ GCG , 0 is the energy density today) and α = − 0 . 22 +0 . 15 − 0 . 13 at the 1 σ con fi dence level using all the datasets. Our results rule out the standard Chaplygin gas model ( α = 1 ) at the 3 σ con fi dence level. The Λ CDM is allowed at the 2 σ con fi dence level. We fi nd that acceleration could have started at a redshift of z ∼ 0 . 70 . The concordance of the generalized Chaplygin gas model with the age estimate of an old high redshift quasar is found. In addition, we show that GRBs can break the degeneracy between the generalized Chaplygin gas model and the XCDM model.
119235128
Gamma-ray burst contributions to constraining the evolution of dark energy
Aims. We explore the gamma-ray bursts' (GRBs') contributions in constraining the dark energy equation of state (EOS) at high (1.8 < z < 7) and at middle redshifts (0.5 < z < 1.8) and estimate how many GRBs are needed to get substantial constraints at high redshifts.
119254658
Deviation from the Cosmological Constant or Systematic Errors
In the work of Qi, Wang & Lu, gamma-ray bursts (GRBs) are used together with an earlier Type Ia supernova (SN Ia) data set to constrain the dark energy equation of state (EOS) in a nearly model-independent way. The improvements made by including GRBs show a slight shift of the dark energy EOS toward w > -1 at redshifts z greater than or similar to 0.5. It is interesting that, when we have more SNe Ia, SNe Ia themselves also show the same trend. Motivated by the fact that both SNe Ia and GRBs seem to prefer a dark energy EOS greater than -1 at redshifts z greater than or similar to 0.5, we perform a careful investigation of this situation, including more careful treatments of measurement errors of GRBs and cross-checking the results by using different ways of including GRBs. We find that the deviation of dark energy from the cosmological constant at redshifts z greater than or similar to 0.5 is large enough that we should pay close attention to it with future observational data. Such a deviation may arise from some biasing systematic errors in the handling of SNe Ia and/or GRBs, or more interestingly from the nature of the dark energy itself.
118676242
Gravitational effects of condensate dark matter on compact stellar objects
We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.
14538301
Measuring dark energy with gamma-ray bursts and other cosmological probes
It has been widely shown that cosmological parameters and dark energy can be constrained by using data from Type Ia supernovae (SNe Ia), the cosmic microwave background (CMB) anisotropy, the baryon acoustic oscillation (BAO) peak from Sloan Digital Sky Survey (SDSS), the X-ray gas mass fraction in clusters, and the linear growth rate of perturbations at z = 0.15 as obtained from the 2dF Galaxy Redshift Survey. Recently, gamma-ray bursts (GRBs) have also been argued to be promising standard candles for cosmography. In this paper, we present constraints on the cosmological parameters and dark energy by combining a recent GRB sample including 69 events with the other cosmological probes. First, we find that for the ΛCDM cosmology this combination makes the constraints stringent, and the best fit is close to the flat universe. Second, we fit the flat Cardassian expansion model and find that this model is consistent with the ΛCDM cosmology. Third, we present constraints on several two-parameter dark energy models and find that these models are also consistent with the ΛCDM cosmology. Finally, we reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We see that the acceleration could have started at a redshift from zt = 0.40 to 0.65. This difference in the transition redshift is due to different dark energy models that we adopt. The most stringent constraint on w(z) lies in the redshift range z ~ 0.3-0.6.
117095291
Preparation of a silicon micro-strip nuclear radiation detector by a two-step annealing process
The annealing process for boron implantation is a crucial step during large size nuclear radiation detector fabrication. It can reduce the lattice defects and the projection straggling. A two-step annealing process for boron implantation was developed instead of a one-step annealing process, and the reverse body resistance of a silicon micro-strip detector was significantly increased, which means that the performance of the detector was improved.
124365356
Current constraints on early dark energy and growth index using latest observations
Aims. In this paper we study observational constraints on early dark energy model proposed by Doran & Robbers and growth index using the latest Union2 type Ia supernovae (SNe Ia), the baryon acoustic oscillations (BAO) in the large-scale correlation function of the Sloan Digital Sky Survey and Two-degree Field Galaxy Redshift Survey, cosmic microwave background (CMB) from the Wilkinson Microwave Anisotropy Probe seven-year data, the linear growth factors data and gamma-ray bursts (GRBs). Methods. By using the χ 2 statics method, we constrain the early dark energy model and growth factor from the above datasets. When including the GRB data, we use the cosmographic parameters to calibrate the GRB luminosity relations using SNe Ia. Results. At 2σ confidence level, we find that the fractional dark energy density at early times is Ω e < 0.05 using SNe Ia, CMB and BAO. When we include high-redshift probes, such as measurements of the linear growth factors and GRBs, the constraint is tightened considerably and becomes Ω e < 0.03 at 2σ confidence level. We also discuss the growth rate index γ .W e f indγ = 0.661 +0.302 −0.203 (1σ) using the SNe Ia, CMB, BAO and linear growth factor data. After including high-redshift GRB data, the growth index is γ = 0.653 +0.372 −0.363 .
18621135
Localization of RF Breakdowns in a Standing Wave Cavity
At SLAC, a 5-cell, normal-conducting, L-band (1.3 GHz), standing-wave (SW) cavity was built as a prototype positron capture accelerator for the ILC. The structure met the ILC gradient goal but required extensive rf processing. When rf breakdowns occurred, a large variation was observed in the decay rate of the stored energy in the cavity after the input power was shut off. It appeared that the breakdowns were isolating sections of the cavity, and that the trapped energy in those sections was then partitioned among its natural modes, producing a distinct beating pattern during the decay. To explore this phenomenon further, an equivalent circuit model of cavity was created that reproduces well its normal operating characteristics. The model was then used to compute the spectra of trapped energy for different numbers of isolated cells. The resulting modal patterns agree well with those of the breakdown data, and thus such a comparison appears to provide a means of identifying the irises on which the breakdowns occurred.
119266561
R-matrix electron-impact excitation data for astrophysically abundant sulphur ions
We present results for the electron-impact excitation of highly-charged sulphur ions (S 8+ –S 11+ ) obtained using the intermediatecoupling frame transformation R-matrix approach. A detailed comparison of the target structure has been made for the four ions to