18 research outputs found
Anisotropic Inflation from Extra Dimensions
Vacuum multidimensional cosmological models with internal spaces being
compact -dimensional Lie group manifolds are considered. Products of
3-spheres and manifold (a novelty in cosmology) are studied. It turns
out that the dynamical evolution of the internal space drives an accelerated
expansion of the external world (power law inflation). This generic solution
(attractor in a phase space) is determined by the Lie group space without any
fine tuning or arbitrary inflaton potentials. Matter in the four dimensions
appears in the form of a number of scalar fields representing anisotropic scale
factors for the internal space. Along the attractor solution the volume of the
internal space grows logarithmically in time. This simple and natural model
should be completed by mechanisms terminating the inflationary evolution and
transforming the geometric scalar fields into ordinary particles.Comment: LaTeX, 11 pages, 5 figures available via fax on request to
[email protected], submitted to Phys. Lett.
Graviton Spectra in String Cosmology
We propose to uncover the signature of a stringy era in the primordial
Universe by searching for a prominent peak in the relic graviton spectrum. This
feature, which in our specific model terminates an increase and
initiates an decrease, is induced during the so far overlooked
bounce of the scale factor between the collapsing deflationary era (or pre-Big
Bang) and the expanding inflationary era (or post-Big Bang). We evaluate both
analytically and numerically the frequency and the intensity of the peak and we
show that they may likely fall in the realm of the new generation of
interferometric detectors. The existence of a peak is at variance with
ordinarily monotonic (either increasing or decreasing) graviton spectra of
canonical cosmologies; its detection would therefore offer strong support to
string cosmology.Comment: 14 pages, RevTex source and 6 figures.p
Inflation in Multidimensional Quantum Cosmology
We extend to multidimensional cosmology Vilenkin's prescription of tunnelling
from nothing for the quantum origin of the observable Universe. Our model
consists of a -dimensional spacetime of topology , with a scalar field (``chaotic inflaton'') for the
matter component. Einstein gravity and Casimir compactification are assumed.
The resulting minisuperspace is 3--dimensional. Patchwise we find an
approximate analytic solution of the Wheeler--DeWitt equation through which we
discuss the tunnelling picture and the probability of nucleation of the
classical Universe with compactifying extra dimensions. Our conclusion is that
the most likely initial conditions, although they do not lead to the
compactification of the internal space, still yield (power-law) inflation for
the outer space. The scenario is physically acceptable because the inner space
growth is limited to in 100 e-foldings of inflation, starting
from the Planck scale.Comment: RevTeX, 30 pages, 4 figures available via fax on request to
[email protected], submitted to Phys. Rev.
A partnership between School and Physics Research. The "Progetto Lauree Scientifiche" al Roma Tre University
Propagation of electromagnetic waves in multidimensional homogeneous cosmologies
SIGLEITItal
Pathophysiology and Main Molecular Mechanisms of Urinary Stone Formation and Recurrence
Kidney stone disease (KSD) is one of the most common urological diseases. The incidence of kidney stones has increased dramatically in the last few decades. Kidney stones are mineral deposits in the calyces or the pelvis, free or attached to the renal papillae. They contain crystals and organic components, and they are made when urine is supersaturated with minerals. Calcium-containing stones are the most common, with calcium oxalate as the main component of most stones. However, many of these form on a calcium phosphate matrix called Randallâs plaque, which is found on the surface of the kidney papilla. The etiology is multifactorial, and the recurrence rate is as high as 50% within 5 years after the first stone onset. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more effective drugs. This review aims to understand the pathophysiology and the main molecular mechanisms known to date to prevent recurrences, which requires behavioral and nutritional interventions, as well as pharmacological treatments that are specific to the type of stone