Marco Bruni                                  GGI Florence, October 2006
Summary
§Non-linear EoS:
worth exploring as dark energy or UDM, has further motivations;
dynamical, effective cosmological constant(s) mostly natural;
Cosmic No-Hair from energy conservation: evolution a-la L-CDM at O(0) in dP/dr(rL) and O(1) in Dr = r - rL , in any theory of gravity.
§Quadratic EoS:
simplest choice beyond linear;
represents truncated Taylor expansion of any  P(r) (3 parameters);
very reach dynamics:
§allows for acceleration with and without rL ;
§Standard and phantom evolution, phantom -> de Sitter (no ÒBig RipÓ);
§Closed models with loitering, or oscillating with no singularity;
singularities are isotropic, as in brane models.
§Affine EoS as UDM pass tests so far and has scalar field equivalent (background).
§Constraints: high z, nucleosynthesis (b>0), perturbations.
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