16 research outputs found
Primordial SdS universe from a 5D vacuum: scalar field fluctuations on Schwarzschild and Hubble horizons
We study scalar field fluctuations of the inflaton field in an early
inflationary universe on an effective 4D Schwarzschild-de Sitter (SdS) metric,
which is obtained after make a planar coordinate transformation on a 5D
Ricci-flat Schwarzschild-de Sitter (SdS) static metric. We obtain the important
result that the spectrum of fluctuations at zeroth order is independent of the
scalar field mass on Schwarzschild scales, while on cosmological scales it
exhibits a mass dependence. However, in the first-order expansion, the spectrum
depends of the inflaton mass and the amplitude is linear with the Black-Hole
(BH) mass .Comment: Final version to be published in JCA
The conformal transformation's controversy: what are we missing?
An alternative interpretation of the conformal transformations of the metric
is discussed according to which the latter can be viewed as a mapping among
Riemannian and Weyl-integrable spaces. A novel aspect of the conformal
transformation's issue is then revealed: these transformations relate
complementary geometrical pictures of a same physical reality, so that, the
question about which is the physical conformal frame, does not arise. In
addition, arguments are given which point out that, unless a clear statement of
what is understood by "equivalence of frames" is made, the issue is a semantic
one. For definiteness, an intuitively "natural" statement of conformal
equivalence is given, which is associated with conformal invariance of the
field equations. Under this particular reading, equivalence can take place only
if the metric is defined up to a conformal equivalence class. A concrete
example of a conformal-invariant theory of gravity is then explored. Since
Brans-Dicke theory is not conformally invariant, then the Jordan's and
Einstein's frames of the theory are not equivalent. Otherwise, in view of the
alternative approach proposed here, these frames represent complementary
geometrical descriptions of a same phenomenon. The different points of view
existing in the literature are critically scrutinized on the light of the new
arguments.Comment: 17 pages, no figures. version accepted by General Relativity and
Gravitation journa