4,137 research outputs found
Constraining Primordial Non-Gaussianity With the Abundance of High Redshift Clusters
We show how observations of the evolution of the galaxy cluster number
abundance can be used to constrain primordial non-Gaussianity in the universe.
We carry out a maximum likelihood analysis incorporating a number of current
datasets and accounting for a wide range of sources of systematic error. Under
the assumption of Gaussianity, the current data prefer a universe with matter
density and are inconsistent with at the
level. If we assume , the predicted degree of cluster
evolution is consistent with the data for non-Gaussian models where the
primordial fluctuations have at least two times as many peaks of height
or more as a Gaussian distribution does. These results are robust to
almost all sources of systematic error considered: in particular, the
Gaussian case can only be reconciled with the data if a number of
systematic effects conspire to modify the analysis in the right direction.
Given an independent measurement of , the techniques described here
represent a powerful tool with which to constrain non-Gaussianity in the
primordial universe, independent of specific details of the non-Gaussian
physics. We discuss the prospects and strategies for improving the constraints
with future observations.Comment: Minor revisions to match published ApJ version, 14 pages emulateap
Scaling solutions in general non-minimal coupling theories
A class of generalized non-minimal coupling theories is investigated, in
search of scaling attractors able to provide an accelerated expansion at the
present time. Solutions are found in the strong coupling regime and when the
coupling function and the potential verify a simple relation. In such cases,
which include power law and exponential functions, the dynamics is independent
of the exact form of the coupling and the potential. The constraint from the
time variability of , however, limits the fraction of energy in the scalar
field to less than 4% of the total energy density, and excludes accelerated
solutions at the present.Comment: 10 pages, 3 figures, accepted for publication in Phys. Rev.
Testing for double inflation with WMAP
With the WMAP data we can now begin to test realistic models of inflation
involving multiple scalar fields. These naturally lead to correlated adiabatic
and isocurvature (entropy) perturbations with a running spectral index. We
present the first full (9 parameter) likelihood analysis of double inflation
with WMAP data and find that despite the extra freedom, supersymmetric hybrid
potentials are strongly constrained with less than 7% correlated isocurvature
component allowed when standard priors are imposed on the cosomological
parameters. As a result we also find that Akaike & Bayesian model selection
criteria rather strongly prefer single-field inflation, just as equivalent
analysis prefers a cosmological constant over dynamical dark energy in the late
universe. It appears that simplicity is the best guide to our universe.Comment: 7 pages, 6 figure
Interacting Agegraphic Dark Energy
A new dark energy model, named "agegraphic dark energy", has been proposed
recently, based on the so-called K\'{a}rolyh\'{a}zy uncertainty relation, which
arises from quantum mechanics together with general relativity. In this note,
we extend the original agegraphic dark energy model by including the
interaction between agegraphic dark energy and pressureless (dark) matter. In
the interacting agegraphic dark energy model, there are many interesting
features different from the original agegraphic dark energy model and
holographic dark energy model. The similarity and difference between agegraphic
dark energy and holographic dark energy are also discussed.Comment: 10 pages, 5 figures, revtex4; v2: references added; v3: accepted by
Eur. Phys. J. C; v4: published versio
Cosmological perturbations from varying masses and couplings
We study the evolution of perturbations during the domination and decay of a
massive particle species whose mass and decay rate are allowed to depend on the
expectation value of a light scalar field. We specialize in the case where the
light field is slow-rolling, showing that during a phase of inhomogeneous
mass-domination and decay the isocurvature perturbation of the light field is
converted into a curvature perturbation with an efficiency which is nine times
larger than when the mass is fixed. We derive a condition on the annihilation
cross section and on the decay rate for the domination of the massive particles
and we show that standard model particles cannot dominate the universe before
nucleosynthesis. We also compare this mechanism with the curvaton model.
Finally, observational signatures are discussed. A cold dark matter
isocurvature mode can be generated if the dark matter is produced out of
equilibrium by both the inflaton and the massive particle species decay.
Non-Gaussianities are present: they are chi-square deviations. However, they
might be too small to be observable.Comment: 21 pages, 4 figures, published versio
Dark Matter and Dark Energy via Non-Perturbative (Flavour) Vacua
A non-perturbative field theoretical approach to flavour physics
(Blasone-Vitiello formalism) has been shown to imply a highly non-trivial
vacuum state. In a previous work, we implemented the approach on a simple
supersymmetric model (free Wess-Zumino), with flavour mixing, which was
regarded as a model for free neutrinos and sneutrinos. The resulting effective
vacuum (called "flavour vacuum") was found to be characterized by a strong SUSY
breaking. In this paper we explore the phenomenology of the model and we argue
that the flavour vacuum is a consistent source for both Dark Energy (thanks to
the bosonic sector of the model) and Dark Matter (via the fermionic one). Quite
remarkably, besides the parameters connected with neutrino physics, in this
model no other parameters have been introduced, possibly leading to a
predictive theory of Dark Energy/Matter. Despite its oversimplification, such a
toy model already seems capable to shed some light on the observed energy
hierarchy between neutrino physics, Dark Energy and Dark Matter. Furthermore,
we move a step forth in the construction of a more realistic theory, by
presenting a novel approach for calculating relevant quantities and hence
extending some results to interactive theories, in a completely
non-perturbative way.Comment: 14 pages, 2 figure
Cosmological dynamics in six-order gravity
We consider cosmological dynamics in generalized modified gravity theory with
the term added to the action of the form . Influence of term to the known solutions of modified gravity is described. We show
that in particular case of these two non-Einstein terms are equally
important on power-law solutions. These solutions and their stability have been
studied using dynamical system approach. Some results for the case of
(including stability of de Sitter solution in the theory under investigation)
have been found using other methods
Cosmological observations in scalar-tensor quintessence
The framework for considering the astronomical and cosmological observations
in the context of scalar-tensor quintessence in which the quintessence field
also accounts for a time dependence of the gravitational constant is developed.
The constraints arising from nucleosynthesis, the variation of the constant,
and the post-Newtonian measurements are taken into account. A simple model of
supernovae is presented in order to extract the dependence of their light
curves with the gravitational constant; this implies a correction when fitting
the luminosity distance. The properties of perturbations as well as CMB
anisotropies are also investigated.Comment: 26 pages, 22 figures, to appear in PR
Carotid artery dissections from TCAR as reported by the Food and Drug Administration
BACKGROUND: Transcarotid artery revascularization (TCAR) is hybrid procedure that allows carotid stenting using direct surgical access of the carotid artery to restore blood flow through the carotid artery. It has shown the lowest perioperative stroke rate when compared with any prospective trial of transfemoral carotid artery stenting. However, intraoperative injuries related to the procedure and its management are not well characterized. We anticipate that this analysis will add qualitative insight in further characterizing adverse outcomes of this novel technology.
METHODS: The FDA maintains a database called the MAUDE (Manufacturer and User Facility Device Experience) for surveillance of all medical devices approved for use. This database was queried for all cases associated with Silk Road Medical’s ENROUTE Transcarotid Neuroprotection System from September 2016 to October 2020.. Case narratives related to patient injuries were individually analyzed to determine type (carotid artery dissection) and time of injury (intraoperative, recovery, post-discharge follow- up). Carotid artery dissection (CD) reporting was further analyzed for associated procedural event at the time of injury, number of access attempts to CD repair, and type of CD repair.
RESUTS: Of the 115 unique incidents in the database, there were 58 CDs. Most were identified intraoperatively (n=55), while 3 were incidentally identified postoperatively. Overall, sheath placement was the most common procedural event attributed to CD (n=34). There was adequate narrative information about CD repair in 54 patients where 52 of them were performed intraoperatively. There were total of 28 endovascular repair and 24 open surgical repairs of CDs from TCAR procedure.
There was no significant difference in rate of endovascular and open surgical repair of CDs that did not need additional access attempts. However, rate of open surgical repair was significantly higher in CDs with persistent failure to engage the true lumen in 2 or more additional access attempts.
Total of 4 strokes were associated with CD. Two occurred during recovery from TCAR admission where one was not intervened per physician’s discretion despite evidence of dissection during the procedure. The other was associated with a fall from a hypotensive event 7 hours after an endovascular CD repair. One incident of stroke occurred intraoperatively during a conversion to CEA as a result of CD. One incident of stroke occurred 4 days after TCAR procedure in which a CD was identified during the stroke evaluation
Conclusion: Carotid artery dissection is the most common injury related to TCAR as reported on MAUDE database. Most common procedural event associated CD was sheath placement. Rate of open surgical repair was significantly higher than endovascular repair in dissections with persistent failure to engage true lumen despite additional access attempts. This should add to qualitative insight among vascular surgery community regarding intraoperative management of carotid artery dissections from a TCAR procedure.https://scholarscompass.vcu.edu/gradposters/1144/thumbnail.jp
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