Parameter estimation of a nonlinear magnetic universe from observations
  The cosmological model consisting of a nonlinear magnetic field obeying the Lagrangian L= \gamma F^{\alpha}, F being the electromagnetic invariant, coupled to a Robertson-Walker geometry is tested with observational data of Type Ia Supernovae, Long Gamma-Ray Bursts and Hubble parameter measurements. The statistical analysis show that the inclusion of nonlinear electromagnetic matter is enough to produce the observed accelerated expansion, with not need of including a dark energy component. The electromagnetic matter with abundance $\Omega_B$, gives as best fit from the combination of all observational data sets \Omega_B=0.562^{+0.037}_{-0.038} for the scenario in which \alpha=-1, \Omega_B=0.654^{+0.040}_{-0.040} for the scenario with \alpha=-1/4 and \Omega_B=0.683^{+0.039}_{-0.043} for the one with \alpha=-1/8. These results indicate that nonlinear electromagnetic matter could play the role of dark energy, with the theoretical advantage of being a mensurable field. 
Ariadna Montiel, Nora Bret\'on and Vincenzo Salzano
astro-ph.CO gr-qc