Dark Energy: the equation of state description versus scalar-tensor or modified gravity

Dark energy dynamics of the universe can be achieved by equivalent mathematical descriptions taking into account generalized fluid equations of state in General Relativity, scalar-tensor theories or modified F(R) gravity in Einstein or Jordan frames. The corresponding technique transforming equation of state description to scalar-tensor or modified gravity is explicitly presented. We show that such equivalent pictures can be discriminated by matching solutions with data capable of selecting the true physical frame.
Comment: LaTeX file, 10 pages, 3 figures, the fit of two equivalent models with observational data is added, new references