Cosmological phase space of R^n gravity

摘要: We present some exact solutions and a phase space analysis of metric $f(R)$-gravity models the type $R^{n}$. divide our discussion in $n\neq2$ $n=2$ models. The later model is good approximation, at late times to $f(R) = \frac{2}{\pi}R \tan^{-1}(R/\beta^2)$ gravity model, being this an example non--singular case. For $n \neq 2$ we have found power law for scale factor that are attractors comply with WMAP 5-years data if <-2.55 $ or 1.67< n < 2$. On other hand, quadratic has de Sitter solution as attractor, also complies data.