151 research outputs found
Anomalous U(1) as a mediator of Supersymmetry Breaking
We point out that an anomalous gauge U(1) symmetry is a natural candidate for
being the mediator and messenger of supersymmetry breaking. It facilitates
dynamical supersymmetry breaking even in the flat limit. Soft masses are
induced by both gravity and the U(1) gauge interactions giving an unusual mass
hierarchy in the sparticle spectrum which suppresses flavor violations. This
scenario does not suffer from the Polonyi problem.Comment: 8 pages, Latex. Some comments adde
Field theory models for variable cosmological constant
Anthropic solutions to the cosmological constant problem require seemingly
unnatural scalar field potentials with a very small slope or domain walls
(branes) with a very small coupling to a four-form field. Here we introduce a
class of models in which the smallness of the corresponding parameters can be
attributed to a spontaneously broken discrete symmetry. We also demonstrate the
equivalence of scalar field and four-form models. Finally, we show how our
models can be naturally embedded into a left-right extension of the standard
model.Comment: A reference adde
â„“-space spectroscopy of the Cosmic Microwave Background with the BOOMERanG experiment
The BOOMERanG experiment has recently produced detailed maps of the Cosmic Microwave Background, where sub-horizon structures are resolved with good signal to noise ratio. A power spectrum (spherical harmonics) analysis of the maps detects three peaks, at multipoles â„“ = (213_(-13)^(+10)),(541_(-32)^(+20))(845_(-25)^(+12)). In this paper we discuss the data analysis and the implications of these results for cosmology
Formation and evolution of cosmic D-strings
We study the formation of D and F-cosmic strings in D-brane annihilation
after brane inflation. We show that D-string formation by quantum de Sitter
fluctuations is severely suppressed, due to suppression of RR field
fluctuations in compact dimensions. We discuss the resonant mechanism of
production of D and F-strings, which are formed as magnetic and electric flux
tubes of the two orthogonal gauge fields living on the world-volume of the
unstable brane. We outline the subsequent cosmological evolution of the D-F
string network. We also compare the nature of these strings with the ordinary
cosmic strings and point out some differences and similarities.Comment: Added discussion and reference
Diluting Cosmological Constant In Infinite Volume Extra Dimensions
We argue that the cosmological constant problem can be solved in a braneworld
model with infinite-volume extra dimensions, avoiding no-go arguments
applicable to theories that are four-dimensional in the infrared. Gravity on
the brane becomes higher-dimensional at super-Hubble distances, which entails
that the relation between the acceleration rate and vacuum energy density flips
upside down compared to the conventional one. The acceleration rate decreases
with increasing the energy density. The experimentally acceptable rate is
obtained for the energy density larger than (1 TeV). The results are stable
under quantum corrections because supersymmetry is broken only on the brane and
stays exact in the bulk of infinite volume extra space. Consistency of 4D
gravity and cosmology on the brane requires the quantum gravity scale to be
around eV. Testable predictions emerging within this approach are:
(i) simultaneous modifications of gravity at sub-millimeter and the Hubble
scales; (ii) Hagedorn-type saturation in TeV energy collisions due to the Regge
spectrum with the spacing equal to eV.Comment: 36 pages, 1 eps fig; 4 refs and comment adde
Global, regional, and national burden of chronic kidney disease, 1990–2017 : a systematic analysis for the Global Burden of Disease Study 2017
Background
Health system planning requires careful assessment of chronic kidney disease (CKD) epidemiology, but data for morbidity and mortality of this disease are scarce or non-existent in many countries. We estimated the global, regional, and national burden of CKD, as well as the burden of cardiovascular disease and gout attributable to impaired kidney function, for the Global Burden of Diseases, Injuries, and Risk Factors Study 2017. We use the term CKD to refer to the morbidity and mortality that can be directly attributed to all stages of CKD, and we use the term impaired kidney function to refer to the additional risk of CKD from cardiovascular disease and gout.
Methods
The main data sources we used were published literature, vital registration systems, end-stage kidney disease registries, and household surveys. Estimates of CKD burden were produced using a Cause of Death Ensemble model and a Bayesian meta-regression analytical tool, and included incidence, prevalence, years lived with disability, mortality, years of life lost, and disability-adjusted life-years (DALYs). A comparative risk assessment approach was used to estimate the proportion of cardiovascular diseases and gout burden attributable to impaired kidney function.
Findings
Globally, in 2017, 1·2 million (95% uncertainty interval [UI] 1·2 to 1·3) people died from CKD. The global all-age mortality rate from CKD increased 41·5% (95% UI 35·2 to 46·5) between 1990 and 2017, although there was no significant change in the age-standardised mortality rate (2·8%, −1·5 to 6·3). In 2017, 697·5 million (95% UI 649·2 to 752·0) cases of all-stage CKD were recorded, for a global prevalence of 9·1% (8·5 to 9·8). The global all-age prevalence of CKD increased 29·3% (95% UI 26·4 to 32·6) since 1990, whereas the age-standardised prevalence remained stable (1·2%, −1·1 to 3·5). CKD resulted in 35·8 million (95% UI 33·7 to 38·0) DALYs in 2017, with diabetic nephropathy accounting for almost a third of DALYs. Most of the burden of CKD was concentrated in the three lowest quintiles of Socio-demographic Index (SDI). In several regions, particularly Oceania, sub-Saharan Africa, and Latin America, the burden of CKD was much higher than expected for the level of development, whereas the disease burden in western, eastern, and central sub-Saharan Africa, east Asia, south Asia, central and eastern Europe, Australasia, and western Europe was lower than expected. 1·4 million (95% UI 1·2 to 1·6) cardiovascular disease-related deaths and 25·3 million (22·2 to 28·9) cardiovascular disease DALYs were attributable to impaired kidney function.
Interpretation
Kidney disease has a major effect on global health, both as a direct cause of global morbidity and mortality and as an important risk factor for cardiovascular disease. CKD is largely preventable and treatable and deserves greater attention in global health policy decision making, particularly in locations with low and middle SDI
A Salmonella Small Non-Coding RNA Facilitates Bacterial Invasion and Intracellular Replication by Modulating the Expression of Virulence Factors
Small non-coding RNAs (sRNAs) that act as regulators of gene expression have been identified in all kingdoms of life, including microRNA (miRNA) and small interfering RNA (siRNA) in eukaryotic cells. Numerous sRNAs identified in Salmonella are encoded by genes located at Salmonella pathogenicity islands (SPIs) that are commonly found in pathogenic strains. Whether these sRNAs are important for Salmonella pathogenesis and virulence in animals has not been reported. In this study, we provide the first direct evidence that a pathogenicity island-encoded sRNA, IsrM, is important for Salmonella invasion of epithelial cells, intracellular replication inside macrophages, and virulence and colonization in mice. IsrM RNA is expressed in vitro under conditions resembling those during infection in the gastrointestinal tract. Furthermore, IsrM is found to be differentially expressed in vivo, with higher expression in the ileum than in the spleen. IsrM targets the mRNAs coding for SopA, a SPI-1 effector, and HilE, a global regulator of the expression of SPI-1 proteins, which are major virulence factors essential for bacterial invasion. Mutations in IsrM result in disregulation of expression of HilE and SopA, as well as other SPI-1 genes whose expression is regulated by HilE. Salmonella with deletion of isrM is defective in bacteria invasion of epithelial cells and intracellular replication/survival in macrophages. Moreover, Salmonella with mutations in isrM is attenuated in killing animals and defective in growth in the ileum and spleen in mice. Our study has shown that IsrM sRNA functions as a pathogenicity island-encoded sRNA directly involved in Salmonella pathogenesis in animals. Our results also suggest that sRNAs may represent a distinct class of virulence factors that are important for bacterial infection in vivo
Nonrestoration of spontaneously broken P, CP and PQ at high temperature
The possibility of P and CP violation at high temperature in models where
these symmetries are spontaneously broken is investigated. It is found that in
minimal models that include singlet fields, high T nonrestoration is possible
for a wide range of parameters of the theory, in particular in models of CP
violation with a CP-odd Higgs field. The same holds true for the invisible
axion version of the Peccei-Quinn mechanism. This can provide both a way out
for the domain wall problem in these theories and the CP violation required for
baryogenesis. In the case of spontaneous P violation it turns out that high T
nonrestoration requires going beyond the minimal model.The results are shown to
hold true when next-to-leading order effects are considered.Comment: 22 pages, 3 figures, uses psfig. Replaced version with the Latex
sourc
Radio emission from negative lightning leader steps reveals inner meter-scale structure
We use the Low Frequency ARray (LOFAR) to probe the dynamics of the stepping process of negatively-charged plasma channels (negative leaders) in a lightning discharge. We observe that at each step of a leader, multiple pulses of VHF (30~--~80 MHz) radiation are emitted in short-duration bursts (<10 μs). This is evidence for streamer formation during corona flashes that occur with each leader step, which has not been observed before in natural lightning and it could help explain X-ray emission from lightning leaders, as X-rays from laboratory leaders tend to be associated with corona flashes. Surprisingly we find that the stepping length is very similar to what was observed near the ground, however with a stepping time that is considerably larger, which as yet is not understood. These results will help to improve lightning propagation models, and eventually lightning protection models
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