1,306 research outputs found
Features in the primordial spectrum: new constraints from WMAP7+ACT data and prospects for Planck
We update the constraints on possible features in the primordial inflationary
density perturbation spectrum by using the latest data from the WMAP7 and ACT
Cosmic Microwave Background experiments. The inclusion of new data
significantly improves the constraints with respect to older work, especially
to smaller angular scales. While we found no clear statistical evidence in the
data for extensions to the simplest, featureless, inflationary model, models
with a step provide a significantly better fit than standard featureless
power-law spectra. We show that the possibility of a step in the inflationary
potential like the one preferred by current data will soon be tested by the
forthcoming temperature and polarization data from the Planck satellite
mission.Comment: V2: 8 pages, 8 figures. Minor changes. Two figures and references
added. Matches version published in Phys. Rev.
The impact of a new median statistics prior on the evidence for dark radiation
Recent analyses that include cosmic microwave background (CMB) anisotropy
measurements from the Atacama Cosmology Telescope and the South Pole Telescope
have hinted at the presence of a dark radiation component at more than two
standard deviations. However, this result depends sensitively on the assumption
of an HST prior on the Hubble constant, where km/s/Mpc at 68%
c.l.. From a median statistics (MS) analysis of 537 non-CMB measurements
from Huchra's compilation we derive km/s/Mpc at 68% c.l., in
good agreement with the results of a recent analysis of the full Huchra list of
measurements. This result is also fully consistent with the value of
km/s/Mpc at 68% c.l. obtained from CMB measurements under
assumption of the standard CDM model. We show that with the MS
prior the evidence for dark radiation is weakened to standard
deviations. Parametrizing the dark radiation component through the effective
number of relativistic degrees of freedom , we find
at 68% c.l. with the HST prior and
at 68% c.l. with the MS prior. We also discuss the implications for current
limits on neutrino masses and on primordial Helium abundances.Comment: 8 pages, 4 figure
Ex-vivo recruitment and x-ray assessment of donor lungs in a challenging retrieval from a donor supported by lvad using the portable normothermic perfusion system: A case report
Lung transplantation (LTx) is limited by the shortage of suitable donors. To overcome this problem, many programs have begun to use donors with extended criteria (marginal donors). However, brain-dead patients with implanted mechanical circulatory support system have rarely been considered as potential lung donors. This case demonstrates the feasibility of lung transplantations from organ donors supported by a mechanical circulatory support system despite the possible difficulties of lung retrieval.
CASE PRESENTATION:
Our case presents a successful procurement and bilateral lung transplantation from a donor supported by a left ventricular assist device (LVAD) who experienced an intraoperatively haemodynamic complication. The use of portable normothermic perfusion device let us to reduce ischemic injury and assess these marginal donor lungs helping us to determine the clinical suitability for transplantation. Given our extensive experience with the device instrumentation and management, the EVLP process was uneventful with excellent post-transplant course.
CONCLUSIONS:
This case report demonstrates the feasibility of lung transplantations from organ donors supported by a mechanical circulatory support system using the portable normothermic perfusion platform to assess and preserve these donor lungs
Constraining Variations in the Fine Structure Constant in the presence of Early Dark Energy
We discuss present and future cosmological constraints on variations of the
fine structure constant induced by an early dark energy component
having the simplest allowed (linear) coupling to electromagnetism. We find that
current cosmological data show no variation of the fine structure constant at
recombination respect to the present-day value, with / =
0.975 \pm 0.020 at 95 % c.l., constraining the energy density in early dark
energy to < 0.060 at 95 % c.l.. Moreover, we consider constraints on
the parameter quantifying the strength of the coupling by the scalar field. We
find that current cosmological constraints on the coupling are about 20 times
weaker than those obtainable locally (which come from Equivalence Principle
tests). However forthcoming or future missions, such as Planck Surveyor and
CMBPol, can match and possibly even surpass the sensitivity of current local
tests.Comment: 5 pages, 3 figure
The Case for Dark Radiation
Combined analyses of recent cosmological data are showing interesting hints
for the presence of an extra relativistic component, coined Dark Radiation.
Here we perform a new search for Dark Radiation, parametrizing it with an
effective number of relativistic degrees of freedom parameter, \neff. We show
that the cosmological data we considered are clearly suggesting the presence
for an extra relativistic component with \neff=4.08_{-0.68}^{+0.71} at 95%
c.l.. Performing an analysis on Dark Radiation sound speed and
viscosity parameters, we found \ceff=0.312\pm0.026 and
\cvis=0.29_{-0.16}^{+0.21} at 95% c.l., consistent with the expectations of a
relativistic free streaming component (\ceff=\cvis=1/3). Assuming the
presence of 3 relativistic neutrinos we constrain the extra relativistic
component with \nnus=1.10_{-0.72}^{+0.79} and \ceff=0.24_{-0.13}^{+0.08} at
95% c.l. while \cvis results as unconstrained. Assuming a massive neutrino
component we obtain further indications for Dark Radiation with
\nnus=1.12_{-0.74}^{+0.86} at 95% c.l. .Comment: 6 pages, 8 figures minor revisions, accepted for publication on PR
Entanglement resolution of free Dirac fermions on a torus
Whenever a system possesses a conserved charge, the density matrix splits
into eigenspaces associated to the each symmetry sector and we can access the
entanglement entropy in a given subspace, known as symmetry resolved
entanglement (SRE). Here, we first evaluate the SRE for massless Dirac fermions
in a system at finite temperature and size, i.e. on a torus. Then we add a
massive term to the Dirac action and we treat it as a perturbation of the
massless theory. The charge-dependent entropies turn out to be equally
distributed among all the symmetry sectors at leading order. However, we find
subleading corrections which depend both on the mass and on the boundary
conditions along the torus. We also study the resolution of the fermionic
negativity in terms of the charge imbalance between two subsystems. We show
that also for this quantity, the presence of the mass alters the equipartition
among the different imbalance sectors at subleading order.Comment: 45 pages, 8 Figure
Future CMB Constraints on Early, Cold, or Stressed Dark Energy
We investigate future constraints on early dark energy (EDE) achievable by
the Planck and CMBPol experiments, including cosmic microwave background (CMB)
lensing. For the dark energy, we include the possibility of clustering through
a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses
parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies
between cosmological parameters and EDE parameters. In particular we show that
the presence of anisotropic stresses in EDE models can substantially undermine
the determination of the EDE sound speed parameter c_s^2. The constraints on
EDE primordial energy density are however unaffected. We also calculate the
future CMB constraints on neutrino masses and find that they are weakened by a
factor of 2 when allowing for the presence of EDE, and highly biased if it is
incorrectly ignored.Comment: 12 pages, 19 figure
The Fine Structure Constant and the CMB Damping Scale
The recent measurements of the Cosmic Microwave Background anisotropies at
arcminute angular scales performed by the ACT and SPT experiments are probing
the damping regime of CMB fluctuations. The analysis of these datasets
unexpectedly suggests that the effective number of relativistic degrees of
freedom is larger than the standard value of Neff = 3.04, and inconsistent with
it at more than two standard deviations. In this paper we study the role of a
mechanism that could affect the shape of the CMB angular fluctuations at those
scales, namely a change in the recombination process through variations in the
fine structure constant. We show that the new CMB data significantly improve
the previous constraints on variations of {\alpha}, with {\alpha}/{\alpha}0 =
0.984 \pm 0.005, i.e. hinting also to a more than two standard deviation from
the current, local, value {\alpha}0. A significant degeneracy is present
between {\alpha} and Neff, and when variations in the latter are allowed the
constraints on {\alpha} are relaxed and again consistent with the standard
value. Deviations of either parameter from their standard values would imply
the presence of new, currently unknown physics.Comment: 4 pages, 1 figur
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