Constraints on cosmological models and reconstructing the acceleration history of the Universe with gamma-ray burst distance indicators
Gamma-ray bursts (GRBs) have been regarded as standard candles at very high redshift for cosmology research. We have proposed a new method to calibrate GRB distance indicators with Type Ia supernova (SNe Ia) data in a completely cosmology-independent way to avoid the circularity problem that had limited the direct use of GRBs to probe cosmology [N. Liang, W.K. Xiao, Y. Liu, and S.N. Zhang,  (2008).]. In this paper, a simple method is provided to combine GRB data into the joint observational data analysis to constrain cosmological models; in this method those SNe Ia data points used for calibrating the GRB data are not used to avoid any correlation between them. We find that the Lambda CDM model is consistent with the joint data in the 1-sigma confidence region, using the GRB data at high redshift calibrated with the interpolating method, the Constitution set of SNe Ia, the cosmic microwave background radiation from Wilkinson Microwave Anisotropy Probe five year observation, the baryonic acoustic oscillation from the spectroscopic Sloan Digital Sky Survey Data Release 7 galaxy sample, the x-ray baryon mass fraction in clusters of galaxies, and the observational Hubble parameter versus redshift data. Comparing to the joint constraints with GRBs and without GRBs, we find that the contribution of GRBs to the joint cosmological constraints is a slight shift in the confidence regions of cosmological parameters to better enclose the Lambda CDM model. Finally, we reconstruct the acceleration history of the Universe up to z > 6 with the distance moduli of SNe Ia and GRBs and find some features that deviate from the Lambda CDM model and seem to favor oscillatory cosmology models; however, further investigations are needed to better understand the situation.

title: Latest cosmological constraints on Cardassian expansion models including the updated gamma-ray bursts
abstract: We constrain the Cardassian expansion models from the latest observations, including the updated Gamma-ray bursts (GRBs), which are calibrated using a cosmology independent method from the Union2 compilation of type Ia supernovae (SNe Ia). By combining the GRB data with the joint observations from the Union2 SNe Ia set, along with the results from the Cosmic Microwave Background radiation observation from the seven-year Wilkinson Microwave Anisotropy Probe and the baryonic acoustic oscillation observation galaxy sample from the spectroscopic Sloan Digital Sky Survey Data Release, we find significant constraints on the model parameters of the original Cardassian model Ω M0 = 0.282 +0.015 -0.014 , n = 0.03 +0.05 -0.05 ; and n = −0.16 +0.25 -3.26 , β = 0.76 +0.34 -0.58 of the modified polytropic Cardassian model, which are consistent with the ΛCDM model in a 1-σ confidence region. From the reconstruction of the deceleration parameter q(z) in Cardassian models, we obtain the transition redshift z T = 0.73 ± 0.04 for the original Cardassian model and z T = 0.68 ± 0.04 for the modified polytropic Cardassian model.

title: Vacuum polarization of scalar electrodynamics in flat space-time with nontrivial topology
abstract: The one-loop vacuum polarization is calculated for scalar electrodynamics in a flat space-time with the topology S1×R3. The effect of vacuum polarization upon photon propagation is considered. It is found that photon propagation becomes anisotropic with some photon modes acquiring a positive topological mass and thus travelling at a subluminal speed.

title: Oscillating universe in the DGP braneworld
abstract: With a method in which the Friedmann equation is written in a form such that evolution of the scale factor can be treated as that of a particle in a potential, we classify all possible cosmic evolutions in the DGP braneworld scenario with the dark radiation term retained. By assuming that the energy component is pressureless matter, radiation or vacuum energy, respectively, we find that in the matter or vacuum energy dominated case, the scale factor has a minimum value ${a}_{0}$. In the matter dominated case, the big bang singularity can be avoided in some special circumstances, and there may exist an oscillating universe or a bouncing one. If the cosmic scale factor is in the oscillating region initially, the universe may undergo an oscillation. After a number of oscillations, it may evolve to the bounce point through quantum tunneling and then expand. However, if the universe contracts initially from an infinite scale, it can turn around and then expand forever. In the vacuum energy dominated case, there exists a stable Einstein static state to avoid the big bang singularity. However, in certain circumstances in the matter or vacuum energy dominated case, a new kind of singularity may occur at ${a}_{0}$ as a result of the discontinuity of the scale factor. In the radiation dominated case, the universe may originate from the big bang singularity, but a bouncing universe which avoids this singularity is also possible.

title: Interacting generalized Chaplygin gas
abstract: A model with the interaction between generalized Chaplygin gas (GCG) and dark matter is studied. We show that the stationary attractor exists and the universe will enter a de Sitter phase in which the energy densities of both the GCG and dark matter are constant. Because of the interaction between the GCG and the dark matter, the equation of state parameter, w, of the GCG can cross the phantom divide and remains less than −1 once crossed. The larger the GCG model parameter α, the earlier the w crosses the divide and the universe enters the accelerating era, and the larger the present value of w and the present acceleration. By investigating the deceleration parameter, we find that a small α is favored by observations.

title: Avoidance of big rip in phantom cosmology by gravitational back reaction
abstract: The effects of the gravitational back reaction of cosmological perturbations are investigated in a cosmological model where the universe is dominated by phantom energy. We assume a COBE normalized spectrum of cosmological fluctuations at the present time and calculate the effective energy–momentum tensor of the gravitational back-reactions of cosmological perturbations whose wavelengths at the time when the back-reactions are evaluated are larger than the Hubble radius. Our results reveal that the effects of gravitational back-reactions will counteract that of phantom energy sooner or later and can become large enough to terminate the phantom dominated phase before the big rip as the universe evolves. This arises because the phase space of infrared modes grows very rapidly as we come close to the big rip.

title: The ASY-EOS experiment at GSI: investigating the symmetry energy at supra-saturation densities
abstract: The elliptic-flow ratio of neutrons with respect to protons in reactions of neutron rich heavy-ions systems at intermediate energies has been proposed as an observable sensitive to the strength of the symmetry term in the nuclear Equation Of State (EOS) at supra-saturation densities. The recent results obtained from the existing FOPI/LAND data for $^{197}$Au+$^{197}$Au collisions at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate of the symmetry term of the EOS but suffer from a considerable statistical uncertainty. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration in May 2011.