683 research outputs found
Minimal Theoretical Uncertainties in Inflationary Predictions
During inflation, primordial energy density fluctuations are created from
approximate de Sitter vacuum quantum fluctuations redshifted out of the horizon
after which they are frozen as perturbations in the background curvature. In
this paper we demonstrate that there exists an intrinsic theoretical
uncertainty in the inflationary predictions for the curvature perturbations due
to the failure of the well known prescriptions to specify the vacuum uniquely.
Specifically, we show that the two often used prescriptions for defining the
initial vacuum state -- the Bunch-Davies prescription and the adiabatic vacuum
prescription (even if the adiabaticity order to which the vacuum is specified
is infinity) -- fail to specify the vacuum uniquely in generic inflationary
spacetimes in which the total duration of inflation is finite. This conclusion
holds despite the absence of any trans-Planckian effects or effective field
theory cutoff related effects. We quantify the uncertainty which is applicable
to slow roll inflationary scenarios as well as for general FRW spacetimes and
find that the uncertainty is generically small. This uncertainty should be
treated as a minimal uncertainty that underlies all curvature perturbation
calculations.Comment: LaTeX file, 35 pages; some typos correcte
Can Inflation solve the Hierarchy Problem?
Inflation with tunneling from a false to a true vacuum becomes viable in the
presence of a scalar field that slows down the initial de Sitter phase. As a
by-product this field also sets dynamically the value of the Newton constant
observed today. This can be very large if the tunneling rate (which is
exponentially sensitive to the barrier) is small enough. Therefore along with
Inflation we also provide a natural dynamical explanation for why gravity is so
weak today. Moreover we predict a spectrum of gravity waves peaked at around
0.1 mHz, that will be detectable by the planned space inteferometer LISA.
Finally we discuss interesting predictions on cosmological scalar and tensor
fluctuations in the light the WMAP 3-year data.Comment: 7 pages. Replaced version with comparison with WMAP 3-year dat
"Swiss-Cheese" Inhomogeneous Cosmology & the Dark Energy Problem
We study an exact swiss-cheese model of the Universe, where inhomogeneous LTB
patches are embedded in a flat FLRW background, in order to see how
observations of distant sources are affected. We find negligible integrated
effect, suppressed by (L/R_{H})^3 (where L is the size of one patch, and R_{H}
is the Hubble radius), both perturbatively and non-perturbatively. We
disentangle this effect from the Doppler term (which is much larger and has
been used recently \cite{BMN} to try to fit the SN curve without dark energy)
by making contact with cosmological perturbation theory.Comment: 35 pages, 6 figure
Light Propagation and Large-Scale Inhomogeneities
We consider the effect on the propagation of light of inhomogeneities with
sizes of order 10 Mpc or larger. The Universe is approximated through a
variation of the Swiss-cheese model. The spherical inhomogeneities are
void-like, with central underdensities surrounded by compensating overdense
shells. We study the propagation of light in this background, assuming that the
source and the observer occupy random positions, so that each beam travels
through several inhomogeneities at random angles. The distribution of
luminosity distances for sources with the same redshift is asymmetric, with a
peak at a value larger than the average one. The width of the distribution and
the location of the maximum increase with increasing redshift and length scale
of the inhomogeneities. We compute the induced dispersion and bias on
cosmological parameters derived from the supernova data. They are too small to
explain the perceived acceleration without dark energy, even when the length
scale of the inhomogeneities is comparable to the horizon distance. Moreover,
the dispersion and bias induced by gravitational lensing at the scales of
galaxies or clusters of galaxies are larger by at least an order of magnitude.Comment: 27 pages, 9 figures, revised version to appear in JCAP, analytical
estimate included, typos correcte
Clinical Support through Telemedicine in Heart Failure Outpatients during the COVID-19 Pandemic Period: Results of a 12-Months Follow Up
Background: Heart failure (HF) patients are predisposed to recurrences and disease destabilizations, especially during the COVID-19 outbreak period. In this scenario, telemedicine could be a proper way to ensure continuous care. The purpose of the study was to compare two modalities of HF outpatients’ follow up, the traditional in-person visits and telephone consultations, during the COVID-19 pandemic period in Italy. Methods: We conducted an observational study on consecutive HF outpatients. The follow up period was 12 months, starting from the beginning of the COVID-19 Italy lockdown. According to the follow up modality, and after the propensity matching score, patients were divided into two groups: those in G1 (n = 92) were managed with traditional in-person visits and those in G2 (n = 92) were managed with telephone consultation. Major adverse cardiovascular events (MACE) were the primary endpoints. Secondary endpoints were overall mortality, cardiovascular death, cardiovascular hospitalization, and hospitalization due to HF. Results: No significant differences between G1 and G2 have been observed regarding MACE (p = 0.65), cardiovascular death (p = 0.39), overall mortality (p = 0.85), hospitalization due to acute HF (p = 0.07), and cardiovascular hospitalization (p = 0.4). Survival analysis performed by the Kaplan–Meier method also did not show significant differences between G1 and G2. Conclusions: Telephone consultations represented a valid option to manage HF outpatients during COVID-19 pandemic, comparable to traditional in-person visits
Isocurvature perturbations in the Ekpyrotic universe
The Ekpyrotic scenario assumes that our visible Universe is a boundary brane
in a five-dimensional bulk and that the hot Big Bang occurs when a nearly
supersymmetric five-brane travelling along the fifth dimension collides with
our visible brane. We show that the generation of isocurvature perturbations is
a generic prediction of the Ekpyrotic Universe. This is due to the interactions
in the kinetic terms between the brane modulus parametrizing the position of
the five-brane in the bulk and the dilaton and volume moduli. We show how to
separate explicitly the adiabatic and isorcuvature modes by performing a
rotation in field space. Our results indicate that adiabatic and isocurvature
pertubations might be cross-correlated and that curvature perturbations might
be entirely seeded by isocurvature perturbations.Comment: 15 pages, LaTeX file, some typos correcte
Effects of different experimental conditions on the PrPSc core generated by protease digestion: implications for strain typing and molecular classification of CJD.
The discovery of molecular subtypes of the pathological prion protein PrPSc has provided the basis for a novel classification of human transmissible spongiform encephalopathies (TSEs) and a potentially powerful method for strain typing. However, there is still a significant disparity regarding the understanding and nomenclature of PrPSc types. In addition, it is still unknown whether a specific PrPSc type is associated with each TSE phenotypic variant. In sporadic Creutzfeldt-Jakob disease (sCJD), five disease phenotypes are known, but only two major types of PrPSc, types 1 and 2, have been consistently reproduced. We further analyzed PrPSc properties in sCJD and variant CJD using a high resolution gel electrophoresis system and varying experimental conditions. We found that pH varies among CJD brain homogenates in standard buffers, thereby influencing the characteristics of protease-treated PrPSc. We also show that PrPSc type 1 and type 2 are heterogeneous species which can be further distinguished into five molecular subtypes that fit the current histopathological classification of sCJD variants. Our results shed light on previous disparities in PrPSc typing, provide a refined classification of human PrPSc types, and support the notion that the pathological TSE phenotype is related to PrPSc structure
Averaging anisotropic cosmologies
We examine the effects of spatial inhomogeneities on irrotational anisotropic
cosmologies by looking at the average properties of anisotropic pressure-free
models. Adopting the Buchert scheme, we recast the averaged scalar equations in
Bianchi-type form and close the standard system by introducing a propagation
formula for the average shear magnitude. We then investigate the evolution of
anisotropic average vacuum models and those filled with pressureless matter. In
the latter case we show that the backreaction effects can modify the familiar
Kasner-like singularity and potentially remove Mixmaster-type oscillations. The
presence of nonzero average shear in our equations also allows us to examine
the constraints that a phase of backreaction-driven accelerated expansion might
put on the anisotropy of the averaged domain. We close by assessing the status
of these and other attempts to define and calculate `average' spacetime
behaviour in general relativity.Comment: revised version, to appear in CQ
Cosmic Microwave Background, Accelerating Universe and Inhomogeneous Cosmology
We consider a cosmology in which a spherically symmetric large scale
inhomogeneous enhancement or a void are described by an inhomogeneous metric
and Einstein's gravitational equations. For a flat matter dominated universe
the inhomogeneous equations lead to luminosity distance and Hubble constant
formulas that depend on the location of the observer. For a general
inhomogeneous solution, it is possible for the deceleration parameter to differ
significantly from the FLRW result. The deceleration parameter can be
interpreted as ( for a flat matter dominated universe) in a
FLRW universe and be as inferred from the inhomogeneous enhancement
that is embedded in a FLRW universe. A spatial volume averaging of local
regions in the backward light cone has to be performed for the inhomogeneous
solution at late times to decide whether the decelerating parameter can be
negative for a positive energy condition. The CMB temperature fluctuations
across the sky can be unevenly distributed in the northern and southern
hemispheres in the inhomogeneous matter dominated solution, in agreement with
the analysis of the WMAP power spectrum data by several authors. The model can
possibly explain the anomalous alignment of the quadrupole and octopole moments
observed in the WMAP data.Comment: 20 pages, no figures, LaTex file. Equations and typos corrected and
references added. Additional material and some conclusions changed. Final
published versio
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