Recently an f （T） gravity based on the modification of teleparallel gravity was proposed to ex-plain the accelerated expansion of the universe. We use observational data from type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background to constrain this f（T） theory and reconstruct the effective equation of state and the deceleration parameter. We obtain the best-fit values of parameters and find an interesting result that the constrained f（T） theory allows for the accelerated Hubble expansion to be a transient effect.
Jing-Zhao QiRong-Jia YangMing-Jian ZhangWen-Biao Liu
Motivated by the recent work that the periodicity of a black hole is responsible for the area spectrum,we exclusively utilize the period of motion of an outgoing wave,which is shown to be related to the vibrational frequency of the perturbed black hole,to study area spectra of a non-rotating BTZ black hole and a rotating BTZ black hole.It is found that the area spectra and entropy spectra for both space times are equally spaced.In addition,we find that though the entropy spectra of the 3-dimensional BTZ black holes take the same form as those of the 4-dimensional black holes,the area spectra depend on the dimension of space times.Our result confirms that the entropy spectrum of a black hole is more fundamental than the area spectrum.
According to Bohr-Sommerfeld quantization rule,an equally spaced horizon area spectrum of a static,spherically symmetric black hole was obtained under an adiabatic invariant action.This method can be extended to the rotating black holes.As an example,this method is applied to the rotating BTZ black hole and the quantized spectrum of the horizon area is obtained.It is shown that the area spectrum of the rotating BTZ black hole is also equally spaced and irrelevant to the rotating parameter,which is consistent with the Bekenstein conjecture.Specifically,the derivation does not need the quasinormal frequencies and the small angular momentum limit.
The recent work of Nation et al., in which the Hawking radiation energy and entropy flow from a black hole is considered to be produced in a one-dimensional Landauer transport process, is extended to the case of a Reissner- Nordstrom black hole. The energy flow contains not only the contribution of the thermal flux but also that of the particle flux. It is found that the charge can also be transported via the one-dimensional quantum tunnel. Because of the existence of the electrostatic potential, the entropy production rate is shown to be smaller than that of the Schwarzschild black hole.
Redshift drift is a tool to directly probe the expansion history of the uni- verse. Based on the Friedmann-Robertson-Walker framework, we reconstruct the ve- locity drift and deceleration factor for several cosmological models using observa- tional H（z） data from the differential ages of galaxies and baryon acoustic oscillation peaks, luminosity distance of Type Ia supernovae, cosmic microwave background shift parameter, and baryon acoustic oscillation distance parameter. They can, for the first time, provide an objective and quantifiable measure of the redshift drift. We find that reconstructed velocity drift with different peak values and corresponding redshifts can potentially provide a method to distinguish the quality of competing dark energy mod- els at low redshifts. Better fitting between models and observational data indicate that current data are insufficient to distinguish the quality of these models. However, by comparing with the simulated velocity drift from Liske et al, we find that the Dvali- Gabadadze-Porrati model is inconsistent with the data at high redshift, which origi- nally piqued the interest of researchers in the topic of redshift drift. Considering the deceleration factor, we are able to give a stable instantaneous estimation of a transition redshift of zt ~ 0.7 from joint constraints, which incorporates a more complete set of values than the previous study that used a single data set.
