1,817 research outputs found
Cosmic Acceleration from Causal Backreaction with Recursive Nonlinearities
We revisit the causal backreaction paradigm, in which the need for Dark
Energy is eliminated via the generation of an apparent cosmic acceleration from
the causal flow of inhomogeneity information coming in towards each observer
from distant structure-forming regions. This second-generation formalism
incorporates "recursive nonlinearities": the process by which
already-established metric perturbations will then act to slow down all future
flows of inhomogeneity information. Here, the long-range effects of causal
backreaction are now damped, weakening its impact for models that were
previously best-fit cosmologies. Nevertheless, we find that causal backreaction
can be recovered as a replacement for Dark Energy via the adoption of larger
values for the dimensionless `strength' of the clustering evolution functions
being modeled -- a change justified by the hierarchical nature of clustering
and virialization in the universe, occurring on multiple cosmic length scales
simultaneously. With this, and with one new model parameter representing the
slowdown of clustering due to astrophysical feedback processes, an alternative
cosmic concordance can once again be achieved for a matter-only universe in
which the apparent acceleration is generated entirely by causal backreaction
effects. One drawback is a new degeneracy which broadens our predicted range
for the observed jerk parameter , thus removing what had
appeared to be a clear signature for distinguishing causal backreaction from
Cosmological Constant CDM. As for the long-term fate of the universe,
incorporating recursive nonlinearities appears to make the possibility of an
`eternal' acceleration due to causal backreaction far less likely; though this
does not take into account gravitational nonlinearities or the large-scale
breakdown of cosmological isotropy, effects not easily modeled within this
formalism.Comment: 53 pages, 7 figures, 3 tables. This paper is an advancement of
previous research on Causal Backreaction; the earlier work is available at
arXiv:1109.4686 and arXiv:1109.515
Update on Biological Therapeutics for Asthma
ABSTRACT: Asthma poses a significant burden on patients, families, health care providers, and the medical system. While efforts to standardize care through guidelines have expanded, difficulty in managing severe asthma has encouraged research about its pathobiology and treatment options. Novel biologic therapeutics are being developed for the treatment of asthma and are of potential use for severe refractory asthma, especially where the increased cost of such agents is more likely justified. This review will summarize currently approved (omalizumab) and investigational biologic agents for asthma, such as antibodies, soluble receptors, and other protein-based antagonists, and highlight recent published data on efficacy and safety of these therapies in humans. As these newer agents with highly targeted pharmacology are tested in asthma, we are also poised to learn more about the role of cytokines and other molecules in the pathophysiology of asthma
Symmetric spaces of higher rank do not admit differentiable compactifications
Any nonpositively curved symmetric space admits a topological
compactification, namely the Hadamard compactification. For rank one spaces,
this topological compactification can be endowed with a differentiable
structure such that the action of the isometry group is differentiable.
Moreover, the restriction of the action on the boundary leads to a flat model
for some geometry (conformal, CR or quaternionic CR depending of the space).
One can ask whether such a differentiable compactification exists for higher
rank spaces, hopefully leading to some knew geometry to explore. In this paper
we answer negatively.Comment: 13 pages, to appear in Mathematische Annale
Wiener algebra for the quaternions
We define and study the counterpart of the Wiener algebra in the quaternionic
setting, both for the discrete and continuous case. We prove a Wiener-L\'evy
type theorem and a factorization theorem. We give applications to Toeplitz and
Wiener-Hopf operators
Convolution-type derivatives, hitting-times of subordinators and time-changed -semigroups
In this paper we will take under consideration subordinators and their
inverse processes (hitting-times). We will present in general the governing
equations of such processes by means of convolution-type integro-differential
operators similar to the fractional derivatives. Furthermore we will discuss
the concept of time-changed -semigroup in case the time-change is
performed by means of the hitting-time of a subordinator. We will show that
such time-change give rise to bounded linear operators not preserving the
semigroup property and we will present their governing equations by using again
integro-differential operators. Such operators are non-local and therefore we
will investigate the presence of long-range dependence.Comment: Final version, Potential analysis, 201
Wormholes as Basis for the Hilbert Space in Lorentzian Gravity
We carry out to completion the quantization of a Friedmann-Robertson-Walker
model provided with a conformal scalar field, and of a Kantowski-Sachs
spacetime minimally coupled to a massless scalar field. We prove that the
Hilbert space determined by the reality conditions that correspond to
Lorentzian gravity admits a basis of wormhole wave functions. This result
implies that the vector space spanned by the quantum wormholes can be equipped
with an unique inner product by demanding an adequate set of Lorentzian reality
conditions, and that the Hilbert space of wormholes obtained in this way can be
identified with the whole Hilbert space of physical states for Lorentzian
gravity. In particular, all the normalizable quantum states can then be
interpreted as superpositions of wormholes. For each of the models considered
here, we finally show that the physical Hilbert space is separable by
constructing a discrete orthonormal basis of wormhole solutions.Comment: 23 pages (Latex), Preprint IMAFF-RC-04-94, CGPG-94/5-
Estimates in Beurling--Helson type theorems. Multidimensional case
We consider the spaces of functions on the
-dimensional torus such that the sequence of the Fourier
coefficients belongs to
. The norm on is defined by
. We study the rate of
growth of the norms as
for -smooth real
functions on (the one-dimensional case was investigated
by the author earlier). The lower estimates that we obtain have direct
analogues for the spaces
Weyl group multiple Dirichlet series constructed from quadratic characters
We construct multiple Dirichlet series in several complex variables whose
coefficients involve quadratic residue symbols. The series are shown to have an
analytic continuation and satisfy a certain group of functional equations.
These are the first examples of an infinite collection of unstable Weyl group
multiple Dirichlet series in greater than two variables.Comment: incorporated referee's comment
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