Motivated by an updated compilation of observational Hubble data (OHD) which consist of 51 points in the redshift range 0.07 < z < 2.36, we study an interesting model known as Cardassian which drives the late cosmic acceleration without a dark energy component. Our compilation contains 31 data points measured with the differential age method by Jimenez & Loeb (2002), and 20 data points obtained from clustering of galaxies. We focus on two modified Friedmann equations: the original Cardassian (OC) expansion and the modified polytropic Cardassian (MPC). The dimensionless Hubble, E(z), and the deceleration parameter, q(z), are revisited in order to constrain the OC and MPC free parameters, first with the OHD and then contrasted with recent observations of SN Ia using the compressed and full joint-light-analysis (JLA) samples. We also perform a joint analysis using the combination OHD plus compressed JLA. Our results show that the OC and MPC models are in agreement with the standard cosmology and naturally introduce a cosmological-constant-like extra term in the canonical Friedmann equation with the capability of accelerating the Universe without dark energy.

Inspired by a new compilation of strong lensing systems, which consist of 204 points in the redshift range 0.0625 &lt; zl &lt; 0.958 for the lens and 0.196 &lt; zs &lt; 3.595 for the source, we constrain three models that generate a late cosmic acceleration: the ω-cold dark matter model, the Chevallier-Polarski-Linder and the Jassal-Bagla-Padmanabhan parametrizations. Our compilation contains only those systems with early type galaxies acting as lenses, with spectroscopically measured stellar velocity dispersions, estimated Einstein radius, and both the lens and source redshifts. We assume an axially symmetric mass distribution in the lens equation, using a correction to alleviate differences between the measured velocity dispersion (σ) and the dark matter halo velocity dispersion (σDM) as well as other systematic errors that may affect the measurements. We have considered different sub-samples to constrain the cosmological parameters of each model. Additionally, we generate a mock data of SLS to asses the impact of the chosen mass profile on the accuracy of Einstein radius estimation. Our results show that cosmological constraints are very sensitive to the selected data: some cases show convergence problems in the estimation of cosmological parameters (e.g. systems with observed distance ratio Dobs &lt; 0.5), others show high values for the chi-square function (e.g. systems with a lens equation Dobs &gt; 1 or high velocity dispersion σ &gt; 276 km s−1). However, we obtained a fiduciary sample with 143 systems which improves the constraints on each tested cosmological model.

Braneworld models have been proposed as a possible solution to the problem of the accelerated expansion of the Universe. The idea is to dispense the dark energy (DE) and drive the late-time cosmic acceleration with a five-dimensional geometry. Here, we investigate a brane model with variable brane tension as a function of redshift called chrono-brane. We propose the polynomial λ = (1 + z) n function inspired in tracker-scalar-field potentials. To constrain the n exponent we use the latest observational Hubble data from cosmic chronometers, Type Ia Supernovae from the full JLA sample, baryon acoustic oscillations and the posterior distance from the cosmic microwave background of Planck 2015 measurements. A joint analysis of these data estimates n 6.19 which generates a DE-like or cosmological-constant-like term, in the Friedmann equation arising from the extra dimensions. This model is consistent with these data and can drive the Universe to an accelerated phase at late times. PACS numbers: 04.50.-h,98.80.-k