12 research outputs found
Metric Perturbations in Dilaton-Driven Inflation
We compute the spectrum of scalar and tensor metric perturbations generated,
as amplified vacuum fluctuations, during an epoch of dilaton-driven inflation
of the type occurring naturally in string cosmology. In the tensor case the
computation is straightforward while, in the scalar case, it is made delicate
by the appearance of a growing mode in the familiar longitudinal gauge. In
spite of this, a reliable perturbative calculation of perturbations far outside
the horizon can be performed by resorting either to appropriate gauge invariant
variables, or to a new coordinate system in which the growing mode can be
"gauged down". The simple outcome of this complicated analysis is that both
scalar and tensor perturbations exhibit nearly Planckian spectra, whose common
"temperature" is related to some very basic parameters of the string-cosmology
background.Comment: 34 pages, latex, no figure
Gravity wave analogs of black holes
It is demonstrated that gravity waves of a flowing fluid in a shallow basin
can be used to simulate phenomena around black holes in the laboratory. Since
the speed of the gravity waves as well as their high-wavenumber dispersion
(subluminal vs. superluminal) can be adjusted easily by varying the height of
the fluid (and its surface tension) this scenario has certain advantages over
the sonic and dielectric black hole analogs, for example, although its use in
testing quantum effects is dubious. It can be used to investigate the various
classical instabilities associated with black (and white) holes experimentally,
including positive and negative norm mode mixing at horizons. PACS: 04.70.-s,
47.90.+a, 92.60.Dj, 04.80.-y.Comment: 14 pages RevTeX, 5 figures, section VI modifie
Non-minimal coupling of the scalar field and inflation
We study the prescriptions for the coupling constant of a scalar field to the
Ricci curvature of spacetime in specific gravity and scalar field theories. The
results are applied to the most popular inflationary scenarios of the universe;
their theoretical consistency and certain observational constraints are
discussed.Comment: 23 pages, LaTex, no figures, to appear in Physical Review
The scaling evolution of cosmological constant
In quantum field theory the parameters of the vacuum action are subject to
renormalization group running. In particular, the ``cosmological constant'' is
not a constant in a quantum field theory context, still less should be zero. In
this paper we continue with previous work, and derive the particle
contributions to the running of the cosmological and gravitational constants in
the framework of the Standard Model in curved space-time. At higher energies
the calculation is performed in a sharp cut off approximation. We assess, in
two different frameworks, whether the scaling dependences of the cosmological
and gravitational constants spoil primordial nucleosynthesis. Finally, the
cosmological implications of the running of the cosmological constant are
discussed.Comment: 25 pages, 1 figure using axodraw. Extended version. The title and the
part of the discussion concerning a gravitational energy scale modified. The
new section about the role of the cosmological constant in the
anomaly-induced inflation added. Misprint in one reference correcte