193 research outputs found
Cosmological dynamics of Scalar--Tensor Gravity
We study the phase--space of FLRW models derived from Scalar--Tensor Gravity
where the non--minimal coupling is and the effective
potential is . Our analysis allows to unfold many
feature of the cosmology of this class of theories. For example, the evolution
mechanism towards states indistinguishable from GR is recovered and proved to
depend critically on the form of the potential . Also, transient
almost--Friedmann phases evolving towards accelerated expansion and unstable
inflationary phases evolving towards stable ones are found. Some of our results
are shown to hold also for the String-Dilaton action.Comment: 25 pages, 4 figures, 12 tables, submitted to CQ
Irrotational dust with Div H=0
For irrotational dust the shear tensor is consistently diagonalizable with
its covariant time derivative: , if
and only if the divergence of the magnetic part of the Weyl tensor vanishes:
. We show here that in that case, the consistency of the Ricci
constraints requires that the magnetic part of the Weyl tensor itself vanishes:
.Comment: 19 pages. Latex. Also avaliable at
http://shiva.mth.uct.ac.za/preprints/text/lesame2.te
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