CPL Model Research Articles

Tension between SNeIa and BAO: current status and future forecasts

Using real and synthetic Type Ia SNe (SNeIa) and baryon acoustic oscillations (BAO) data representingcurrent observations forecasts, this paper investigates the tension between thoseprobes in the dark energy equation of state (EoS) reconstruction considering thewell known CPL model and Wang's low correlation reformulation. In particular, here we presentsimulations of BAO data from both the the radial andtransverse directions. We also explore the influence of priors on Ωm andΩb on the tension issue, by considering 1σ deviations in either one or bothof them. Our results indicate that for some priors there is no tension between a single dataset(either SNeIa or BAO) and their combination (SNeIa+BAO). Our criterion to discernthe existence of tension (σ-distance) is also useful to establish which is the datasetwith most constraining power; in this respect SNeIa and BAO data switch roles when current andfuture data are considered, as forecasts predict and spectacular quality improvement on BAOdata. We also find that the results on the tension are blind to the way the CPL model isaddressed: there is a perfect match between the original formulation and that by the correlationoptimized proposed in Wang (2008), but the errors on the parameters are much narrowerin all cases of our exhaustive exploration, thus serving the purpose of stressing the convenienceof this reparametrization.

Seeking evolution of dark energy

We study how observationally to distinguish between a cosmological constant (CC) and an evolving dark energy with equation of state $\omega(Z)$. We focus on the value of redshift Z* at which the cosmic late time acceleration begins and $\ddot{a}(Z^{*}) = 0$. Four $\omega(Z)$ are studied, including the well-known CPL model and a new model that has advantages when describing the entire expansion era. If dark energy is represented by a CC model with $\omega \equiv -1$, the present ranges for $\Omega_{\Lambda}(t_0)$ and $\Omega_m(t_0)$ imply that Z* = 0.743 with 4% error. We discuss the possible implications of a model independent measurement of Z* with better accuracy.

Probing the dynamics of dark energy with novel parametrizations

We point out that the CPL parametrization has a problem that the equation of state w(z) diverges in the far future, so that this model can only properly describe the past evolution but cannot depict the future evolution. To overcome such a difficulty, in this Letter we propose two novel parametrizations for dark energy, the logarithm form w(z)=w0+w1(ln(2+z)1+z−ln2) and the oscillating form w(z)=w0+w1(sin(1+z)1+z−sin(1)), successfully avoiding the future divergency problem in the CPL parametrization, and use them to probe the dynamics of dark energy in the whole evolutionary history. Our divergency-free parametrizations are proven to be very successful in exploring the dynamical evolution of dark energy and have powerful prediction capability for the ultimate fate of the universe. Constraining the CPL model and the new models with the current observational data, we show that the new models are more favored. The features and the predictions for the future evolution in the new models are discussed in detail.

Spectral analysis of Swift long gamma-ray bursts with known redshift

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15–150 keV) of the Swift-BAT detector, the spectral fitting is reliable only for fitting models with two or three parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, two parameters) and cut-off power law (CPL, three parameters) models to the time-integrated spectra of the 47 bursts, and we present the corresponding parameters, their uncertainties and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the νfν peak energy Epk. For these GRBs, we calculate the energy fluence and the rest-frame isotropic-equivalent radiated energy, Eγ,iso, as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram E′pk versus Eγ,iso. We confirm a significant correlation between these two quantities (the ‘Amati’ relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high-energy PL index frozen to −2.3, obtaining a rather good agreement with the ‘Amati’ relation of non-Swift GRBs.

Quantizations of the Fermion-Coupled CP1 Model with the Chern-Simons Term: Statistics Transmutation in Commutator Algebra

We consider the Cpl model with the Chern-Simons term coupled to a fermion, which is a possible model of the high- Tc superconductivity. By using the Dirac algorithm, we construct the generalized Hamiltonian formalism for this system and quantize it canonically. The path-integral quantization is also performed following the Faddeev-Senjanovic procedure. On the basis of the quantized system, we show that the bose-fermi transmutation of each field content occurs, by investigating the equal­ time (anti-) commutators.