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The possibility to avoid the cosmic initial singularity as a consequence of nonlinear effects on the Maxwell eletromagnetic theory is discussed. For a flat FRW geometry we derive the general nonsingular solution supported by a magnetic field plus a cosmic fluid and a nonvanishing vacuum energy density.The nonsingular behavior of solutions with a time-dependent Λ(t)-term are also examined. As a general result, it is found that the functional dependence of Λ(t) can uniquely be determined only if the magnetic field remains constant.All these models are examples of bouncing universes which may exhibit an inflationary dynamics driven by the nonlinear corrections of the magnetic field.

The 2-point angular correlation function w(θ) (2PACF), where θ is the angular separation between pairs of galaxies, provides the transversal Baryon Acoustic Oscillation (BAO) signal almost model-independently. In this paper we use 409,337 luminous red galaxies in the redshift range z = [0.440, 0.555] obtained from the tenth data release of the Sloan Digital Sky Survey (SDSS DR10) to estimate θBAO(z) from the 2PACF at six redshift shells. Since noise and systematics can hide the BAO signature in the w − θ plane, we also discuss some criteria to localize the acoustic bump. We identify two sources of model-dependence in the analysis, namely, the value of the acoustic scale from Cosmic Microwave Background (CMB) measurements and the correction in the θBAO(z) position due to projection effects. Constraints on the dark energy equation-of-state parameter w(z) from the θBAO(z) diagram are derived, as well as from a joint analysis with current CMB measurements. We find that the standard ΛCDM model as well as some of its extensions are in good agreement with these θBAO(z) measurements. * Electronic address: gabriela@on.br † Electronic address: bernui@on.br ‡ Electronic address: micolbenetti@on.br § Electronic address: jcarvalho@on.br ¶ Electronic address: alcaniz@on.br 1 The acoustic scale is defined as rs = ∞ z d cs(z) H(z) dz, where z d ≈ 1070 is the redshift of the drag epoch and cs(z) is the sound speed of the photon-baryon fluid. arXiv:1507.08972v2 [astro-ph.CO]

We use current measurements of the expansion rate H(z) and cosmic background radiation bounds on the spatial curvature of the Universe to impose cosmological model-independent constraints on cosmic opacity. To perform our analyses, we compare opacity-free distance modulus from H(z) data with those from two type Ia supernovae compilations, namely, the Union2.1 plus the most distant spectroscopically confirmed SNe Ia (SCP-0401 at z = 1.713) and two Sloan Digital Sky Survey (SDSS) subsamples. We find that a completely transparent universe is in full agreement with the Union 2.1 + SNe Ia SCP-0401 sample. For the SDSS compilations, such universe is compatible with observations at < 1.5σ level regardless the SNe Ia light-curve fitting used.