Observational Constraints On The F(T) Gravity Models And The Cosmic Acceleration

Modern cosmology,based on the theory of general relativity and the principle of cosmology,has made brilliant achievements,but there are still some important theoretical problems that need to be resolved,one of which is the cause of the current cosmic accelerating expansion.One way to explain the cosmic acceleration is by introducing dark energy（DE）,which is an energy component with negative pressure.A large amount of observational data shows that dark energy,if it exists,accounts for about 70%of the energy of the universe.Another is by modifying the theory of general relativity.In this way,we do not need to introduce exotic energy component to explain the current cosmic acceleration.Similar to f（R）gravity,which is constructed basing on the theory of general relativity,f（T）gravity is also a modification of gravity which is constructed basing on the teleparallel gravity.Up to now,many f（T）models have been proposed,and it is found that those models can explain the current cosmic acceleration.Most recently,using the newly released baryon acoustic oscillation（BAO）data,some new and significative properties of DE are found.Thus,it is worth investigating the implication of new BAO data on the modified theories of gravity.Therefore,we perform observational tests on viable f（T）models with BAO measurements,Ia supernova（SNIa）data,the cosmic microwave background（CMB）data,the latest Hubble data（H（z））as well as the local value of Hubble constant（H₀）.We find that although f（T）gravity can explain the current cosmic acceleration,theΛplus cold dark matter（ΛCDM）model is the most favored model by current observations in light of the information criteria.Furthermore,since we can not determine the evolution of the dark energy equation of state w（z）at present,many parameterizations of w（z）are proposed.However,basing on those parameterized dark energy models,there are some ten-sions in studying the cosmic acceleration.For example,theΛCDM model pre-dicts that the expansion of the universe will continue to accelerate,while using the Chevallier-Polarski-Linder（CPL）parameterization（w（z）=w₀+w₁z/（1+z）,where w₀and w₁are two constants）,it was found that the acceleration of the cosmic expansion might be slowing down from the low redshift SNIa+BAO data,but once the high redshift CMB data were added,the observations remain to fa-vor an increasing cosmic acceleration.Thus,we reconstruct the evolution of the deceleration parameter q（z）with a model-independent non-parametric Bayesian method.We find that all data support a currently increasing cosmic acceleration,and since the current observations support a flat universe,the effects of spatial curvature on the evolution of q（z）are negligible.Moreover,the evolution of q（z）has an oscillatory behavior,and compared with the results obtained in theΛCDM,this oscillatory behavior is preferred by observations at the 3.2σconfidence level.Therefore,our results indicate that the slowing down of the cosmic acceleration obtained in previous works should come from an improper parametrization of dark energy equation of state,and the q（z）evolution obtained from theΛCDM may be misleadingly inaccurate.