1,721,091 research outputs found
On some exponential potentials for a cosmological scalar field as quintessence
No full textWe present general exact solutions for two classes of exponential potentials in a scalar
field model for quintessence. The coupling is minimal and we consider only dust
and scalar field. To some extent, it is possible to reproduce experimental results from
supernovae
Quintessence or phoenix?
No full textWe show that it is impossible to determine the state equation of quintessence models on the basis of pure observational SNIa data. An independent estimate of Omega_M0 is necessary. Also in this most favourable case the situation can be problematic
Variable G and Lambda: scalar-tensor versus RG-improved cosmology
No full textWe study the consequences due to time varying G and Lambda in scalar-tensor theories of gravity for cosmology, inspired by the modifications introduced by the Renormalization Group (RG) equations in the Quantum Einstein Gravity. We assume a power-law scale factor in presence contemporarily of both the scalar field and the matter components of the cosmic fluid, and analyze a special case and its generalization, also showing the possibility of a phantom cosmology. In both such situations we find a negative kinetic term for the scalar field Q and, possibly, an equation-of-state parameter w_Q less than −1. A violation of dominant energy condition (DEC) for Q is also possible in both of them; but, while in the first special case the Q-energy density then remains positive, in the second one we find it negative
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