Torsional Gravity And Dynamical Evolution Of Universe

The exploration of the dynamical history of the universe combined with experimental observation is very important.On the one hand,we need to use the new model to explain new phenomena that existing theory cannot explain.On the other hand,We need to constrain and reconstruct the corresponding theoretical model by observational data.We also need to guarantee the consistency of a theory and look for observation effects that can be used to test the theory on different scales.We first consider the torsional gravity in a cosmological framework to alter the background evolution.Then we use the latest H0 measurement from the SH0ES Team as well as observational Hubble data to reconstruct the f(T)model in a modelindependent way by applying Gaussian processes.Since the special square-root term does not affect the evolution at the background level,we finally summarize a family of functions that can produce the background evolution required by the data.Finally,performing a fitting using polynomial functions we find an analytic expression that may describe the cosmological evolution in great agreement with observations.We further use a combination of observational data in order to reconstruct the free function of f(T)gravity in this model-independent manner.Starting from the data-driven determined dark-energy equation-of-state parameter we are able to reconstruct the f(T)form.The obtained function is consistent with the standard ACDM(Lambda cold dark matter)cosmology within 1σ confidence level,however the best-fit value experiences oscillatory features.We parametrise it with a sinusoidal function,which is a small oscillatory deviation from ACDM paradigm.Similar oscillatory dark-energy scenarios are known to be in good agreement with observational data,nevertheless this is the first time that such a behavior is proposed for f(T)gravity.Finally,since the reconstruction procedure is completely model-independent,the obtained data-driven reconstructed f(T)form could release the H0 tensions between ACDM estimations and local measurements.In order to explain the 21-cm line global signal at the epoch of cosmic dawn by EDGES(the Experiment to Detect the Global Epoch of Reionization Signature).We firstly analyze two dynamical mechanisms in which different background evolutions can exert considerable effects on the 21-cm line global signal.One of them is the change in decoupling time of Compton scattering heating,the other stems from the direct change of optical depth due to the different expansion rate of the Universe.We study the influence of linear interacting dark energy models and early dark energy on 21-cm line signal.we find that the optical depth can be significantly changed by interacting dark energy.While,the early dark energy models which only influences the evolution of the cosmic background at specific stages in the early time can obtain earlier decoupling time of Compton scattering heating.Eventually,we fulfill EDGES data by adding an early dark energy dominated stage to the cosmological paradigm described by IDE models.While taking the current experimental constraints on the parameter space into account,this kind of model still has trouble giving rise to a strong enough signal reported by EDGES.We also calculate the deflection angle,as well as the positions and magnifications of the lensed images,in the case of covariant f(T)gravity.We first extract the spherically symmetric solutions for both the pure-tetrad and the covariant formulation of the theory,since considering spherical solutions the extension to the latter is crucial,in order for the results not to suffer from frame-dependent artifacts.Applying the perturbative approximation we extract the deviations of the solutions comparing to General Relativity.Furthermore,we calculate the deflection angle and then the differences of the positions and magnifications in the lensing framework.This effect of consistent f(T)gravity on the lensing features can serve as an observable signature in the realistic cases where f(T)is expected to deviate only slightly from General Relativity,since lensing scales in general are not restricted as in the case of Solar System data,and therefore deviations from General Relativity could be observed more easily.