1,504 research outputs found
Thermal Relics in Modified Cosmologies: Bounds on Evolution Histories of the Early Universe and Cosmological Boosts for PAMELA
Alternative cosmologies, based on extensions of General Relativity, predict
modified thermal histories in the Early Universe during the pre Big Bang
Nucleosynthesis (BBN) era, epoch which is not directly constrained by
cosmological observations. When the expansion rate is enhanced with respect to
the standard case, thermal relics typically decouple with larger relic
abundances. The correct value of the relic abundance is therefore obtained for
larger annihilation cross--sections, as compared to standard cosmology. A
direct consequence is that indirect detection rates are enhanced. Extending
previous analyses of ours, we derive updated astrophysical bounds on the dark
matter annihilation cross sections and use them to constrain alternative
cosmologies in the pre--BBN era. We also determine the characteristics of these
alternative cosmologies in order to provide the correct value of relic
abundance for a thermal relic for the (large) annihilation cross--section
required to explain the PAMELA results on the positron fraction, therefore
providing a "cosmological boost" solution to the dark matter interpretation of
the PAMELA data.Comment: 19 pages, 27 figures, matches published versio
Prosthetic abdominal wall hernia repair in emergency surgery: from polypropylene to biological meshes
The use of nonabsorbable prosthetic materials such as polypropylene, polyester, and ePTFE, have expanded and are now widely used in reparative surgery for abdominal wall hernias
Axion-Dilaton Cosmology and Dark Energy
We discuss a class of flat FRW cosmological models based on D=4 axion-dilaton
gravity universally coupled to cosmological background fluids. In particular,
we investigate the possibility of recurrent acceleration, which was recently
shown to be generically realized in a wide class of axion-dilaton models, but
in absence of cosmological background fluids. We observe that, once we impose
the existence of radiation -and matter- dominated earlier stages of cosmic
evolution, the axion-dilaton dynamics is altered significantly with respect to
the case of pure axion-dilaton gravity. During the matter dominated epoch the
scalar fields remain either frozen, due to the large expansion rate, or enter a
cosmological scaling regime. In both cases, oscillations of the effective
equation of state around the acceleration boundary value are impossible. Models
which enter an oscillatory stage in the low redshift regime, on the other hand,
are disfavored by observations. We also comment on the viability of the
axion-dilaton system as a candidate for dynamical dark energy. In a certain
subclass of models, an intermediate scaling regime is succeeded by eternal
acceleration. We also briefly discuss the issue of dependence on initial
conditions.Comment: 28 pages, 11 figure
Analyzing Direct Dark Matter Detection Data by the AMIDAS Website
In this talk I have presented the data analysis results of extracting
properties of halo WIMPs: the mass and the (ratios between the)
spin-independent and spin-dependent couplings/cross sections on nucleons by the
AMIDAS website. Although non-standard astronomical setup has been used to
generate pseudodata sets for our analyses, it has been found that, without
prior information/assumption about the local density and velocity distribution
of halo Dark Matter, these WIMP properties have been reconstructed with ~5% to
< ~40% deviations from the input values.Comment: 12 pages, 8 eps figures, 1 table, to appear in the proceedings of the
3rd Workshop on Directional Detection of Dark Matter (CYGNUS 2011), June
7-10, 2011, Aussois, Franc
Dark Matter Relic Abundance and Scalar-Tensor Dark Energy
Scalar-tensor theories of gravity provide a consistent framework to
accommodate an ultra-light quintessence scalar field. While the equivalence
principle is respected by construction, deviations from General Relativity and
standard cosmology may show up at nucleosynthesis, CMB, and solar system tests
of gravity. After imposing all the bounds coming from these observations, we
consider the expansion rate of the universe at WIMP decoupling, showing that it
can lead to an enhancement of the dark matter relic density up to few orders of
magnitude with respect to the standard case. This effect can have an impact on
supersymmetric candidates for dark matter.Comment: 12 pages, 13 figures; V2: references added, matches published versio
Dynamical Relaxation of the Dark Matter to Baryon Ratio
A scalar field interacting differently with dark matter and baryons may
explain why their ratio is of order unity today. We provide three working
examples, checking them against the observations of CMB, Large Scale Structure,
supernovae Ia, and post-newtonian tests of gravity. Such a scenario could make
life much easier for supersymmetric dark matter candidates.Comment: 7 pages, 5 .eps figures. Discussion of the approach of the field to
the fixed point added. Figures modified accordingly. Conclusions unchanged.
Version to be published on Phys Rev.
Emergency surgery for recurrent intraabdominal cancer
Recurrent abdominal cancer can manifest in many ways but there are certain situations that are a great challenge to clinicians. Emergency presentation is one such situation. Surgeons are faced with a therapeutic dilemma that on the one hand most of these patients have a limited life expectancy, and on the other surgical procedures are unavoidable. We reviewed our experience of recurrent abdominal cancers presenting with acute abdominal symptoms requiring emergency
Probing the stability of superheavy dark matter particles with high-energy neutrinos
Two of the most fundamental properties of the dark matter particle, the mass
and the lifetime, are only weakly constrained by the astronomical and
cosmological evidence of dark matter. We derive in this paper lower limits on
the lifetime of dark matter particles with masses in the range 10 TeV-10^15 TeV
from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube,
Auger and ANITA experiments. For dark matter particles which produce neutrinos
in a two body or a three body decay, we find that the dark matter lifetime must
be longer than O(10^26-10^28) s for masses between 10 TeV and the Grand
Unification scale. Finally, we also calculate, for concrete particle physics
scenarios, the limits on the strength of the interactions that induce the dark
matter decay.Comment: 17 pages, 6 figures; v2: references added, discussion improved,
matches the version published at JCA
Insulin Resistance and High Blood Pressure: Mechanistic Insight on the Role of the Kidney
The metabolic effects of insulin predominate in skeletal muscle, fat, and liver where the hormone binds to its receptor, thereby priming a series of cell-specific and biochemically diverse intracellular mechanisms. In the presence of a good secretory reserve in the pancreatic islets, a decrease in insulin sensitivity in the metabolic target tissues leads to compensatory hyperinsulinemia. A large body of evidence obtained in clinical and experimental studies indicates that insulin resistance and the related hyperinsulinemia are causally involved in some forms of arterial hypertension. Much of this involvement can be ascribed to the impact of insulin on renal sodium transport, although additional mechanisms might be involved. Solid evidence indicates that insulin causes sodium and water retention, and both endogenous and exogenous hyperinsulinemia have been correlated to increased blood pressure. Although important information was gathered on the cellular mechanisms that are triggered by insulin in metabolic tissues and on their abnormalities, knowledge of the insulin-related mechanisms possibly involved in blood pressure regulation is limited. In this review, we summarize the current understanding of the cellular mechanisms that are involved in the pro-hypertensive actions of insulin, focusing on the contribution of insulin to the renal regulation of sodium balance and body fluids
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