Cosmology in a reduced Born-Infeld--$f(T)$ theory of gravity

Abstract

A perfect fluid, spatially flat cosmology in a $f(T)$ model, derived from a recently proposed general Born-Infeld type theory of gravity is studied. Four dimensional cosmological solutions are obtained assuming the equation of state $p=ωρ$. For a positive value of $λ$ (a parameter in the theory) the solution is singular (of big-bang type) but may have accelerated expansion at an early stage. For $λ<0$ there exists a non-zero minimum scale factor and a finite maximum value of the energy density, but the curvature scalar diverges. Interestingly, for $λ<0$, the universe may undergo an eternal accelerated expansion with a de Sitter expansion phase at late times. We find these features without considering any extra matter field or even negative pressure. Fitting our model with Supernova data we find that the simplest dust model ($p=0$), with $λ>0$, is able to generate acceleration and fits well, although the resulting properties of the universe differ much from the known, present day, accepted values. The best fit model requires (with $λ> 0$) an additional component of the physical matter density, with a negative value of the equation of state parameter, along with dust. The $λ< 0$ solutions do not fit well with observations. Though these models do not explain the dark energy problem with consistency, their analysis does shed light on the plausibility of an alternative geometrical explanation.