1,970 research outputs found
Models of G time variations in diverse dimensions
A review of different cosmological models in diverse dimensions leading to a
relatively small time variation of the effective gravitational constant G is
presented. Among them: 4-dimensional general scalar-tensor model,
multidimensional vacuum model with two curved Einstein spaces, multidimensional
model with multicomponent anisotropic "perfect fluid", S-brane model with
scalar fields and two form field etc. It is shown that there exist different
possible ways of explanation of relatively small time variation of the
effective gravitational constant G compatible with present cosmological data
(e.g. acceleration): 4-dimensional scalar-tensor theories or multidimensional
cosmological models with different matter sources. The experimental bounds on
G-dot may be satisfied ether in some restricted interval or for all allowed
values of the synchronous time variable.Comment: 27 pages, Late
Composite S-Brane Solutions On Product Of Ricci-Flat Spaces
A family of generalized -brane solutions with orthogonal intersection
rules and Ricci-flat factor spaces in the theory with several scalar fields
and antisymmetric forms is considered. Two subclasses of solutions with
power-law and exponential behaviour of scale factors are singled out. These
subclasses contain sub-families of solutions with accelerated expansion of
certain factor spaces. The solutions depend on charge densities of branes,
their dimensions and intersections, dilatonic couplings and the number of
dilatonic fields.Comment: To appear in GR
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