The cosmological constant problem in codimension-two brane models

We discuss the possibility of a dynamical solution to the cosmological constant problem in the contaxt of six-dimensional Einstein-Maxwell theory. A definite answer requires an understanding of the full bulk cosmology in the early universe, in which the bulk has time-dependent size and shape. We comment on the special properties of codimension two as compared to higher codimensions.Comment: 11 page

The General Warped Solution with Conical Branes in Six-dimensional Supergravity

We present the general regular warped solution with 4D Minkowski spacetime in six-dimensional gauged supergravity. In this framework, we can easily embed multiple conical branes into the warped geometry by choosing an undetermined holomorphic function. As an example, for the holomorphic function with many zeroes, we find warped solutions with multi-branes and discuss the generalized flux quantization in this case.Comment: 1+19 pages, no figure, JHEP style, version to appear in JHE

4d-Flat Compactifications With Brane Vorticities

We present solutions in six-dimensional gravity coupled to a sigma model, in the presence of three-brane sources. The space transverse to the branes is a compact non-singular manifold. The example of O(3) sigma model in the presence of two three-branes is worked out in detail. We show that the four-dimensional flatness is obtained with a single condition involving the brane tensions, which are in general different and may be both positive, and another characteristic of the branes, vorticity. We speculate that the adjustment of the effective four-dimensional cosmological constant may occur through the exchange of vorticity between the branes. We then give exact instanton type solutions for sigma models targeted on a general K\"ahler manifold, and elaborate in this framework on multi-instantons of the O(3) sigma model. The latter have branes, possibly with vorticities, at the instanton positions, thus generalizing our two-brane solution.Comment: 8 pages. New references added and minor typos are correcte

Cosmological Evolution of a Purely Conical Codimension-2 Brane World

We study the cosmological evolution of isotropic matter on an infinitely thin conical codimension-two brane-world. Our analysis is based on the boundary dynamics of a six-dimensional model in the presence of an induced gravity term on the brane and a Gauss-Bonnet term in the bulk. With the assumption that the bulk contains only a cosmological constant Lambda_B, we find that the isotropic evolution of the brane-universe imposes a tuned relation between the energy density and the brane equation of state. The evolution of the system has fixed points (attractors), which correspond to a final state of radiation for Lambda_B=0 and to de Sitter state for Lambda_B>0. Furthermore, considering anisotropic matter on the brane, the tuning of the parameters is lifted, and new regions of the parametric space are available for the cosmological evolution of the brane-universe. The analysis of the dynamics of the system shows that, the isotropic fixed points remain attractors of the system, and for values of Lambda_B which give acceptable cosmological evolution of the equation of state, the line of isotropic tuning is a very weak attractor. The initial conditions, in this case, need to be fine tuned to have an evolution with acceptably small anisotropy.Comment: 20 pages, 4 figures, typo correcte

The 6D SuperSwirl

We present a novel supersymmetric solution to a nonlinear sigma model coupled to supergravity. The solution represents a static, supersymmetric, codimension-two object, which is different to the familiar cosmic strings. In particular, we consider 6D chiral gauged supergravity, whose spectrum contains a number of hypermultiplets. The scalar components of the hypermultiplet are charged under a gauge field, and supersymmetry implies that they experience a simple paraboloid-like (or 2D infinite well) potential, which is minimised when they vanish. Unlike conventional vortices, the energy density of our configuration is not localized to a string-like core. The solutions have two timelike singularities in the internal manifold, which provide the necessary boundary conditions to ensure that the scalars do not lie at the minimum of their potential. The 4D spacetime is flat, and the solution is a continuous deformation of the so-called ``rugby ball'' solution, which has been studied in the context of the cosmological constant problem. It represents an unexpected class of supersymmetric solutions to the 6D theory, which have gravity, gauge fluxes and hyperscalars all active in the background.Comment: 26 pages, 2 figures, JHEP3 class. Typos corrected, analysis expanded, references adde

Pseudo-3-Branes in a Curved 6D Bulk

We consider a model involving a 4-brane in a 6D bulk which carries sigma model fields. An axion field on the 4-brane cancels the pressure along one direction leading to an effective codimension-2 3-brane. For a range of parameters of the theory, we get a transverse space which is non-compact, providing a possible solution to the cosmological constant problem. A setup with two branes in a compact space is also treated. In this case, a mild fine-tuning between the radii of the two 4-branes is necessary. Finally, we explore the 4-brane problem in the Gauss-Codazzi formulation and we discuss general aspects of gravity in the presence of additional brane sources.Comment: 13 page

Gravity on codimension 2 brane worlds

We compute the matching conditions for a general thick codimension 2 brane, a necessary previous step towards the investigation of gravitational phenomena in codimension 2 braneworlds. We show that, provided the brane is weakly curved, they are specified by the integral in the extra dimensions of the brane energy-momentum, independently of its detailed internal structure. These general matching conditions can then be used as boundary conditions for the bulk solution. By evaluating Einstein equations at the brane boundary we are able to write an evolution equation for the induced metric on the brane depending only on physical brane parameters and the bulk energy-momentum tensor. We particularise to a cosmological metric and show that a realistic cosmology can be obtained in the simplest case of having just a non-zero cosmological constant in the bulk. We point out several parallelisms between this case and the codimension 1 brane worlds in an AdS space.Comment: 24 page

Formats: Abstract | Full Text | PDF (149K) Can J Infect Dis

Abstract OBJECTIVE: To discuss the occurrence of genital chlamydia in developed countries and review the literature assessing the potential risk factors for this sexually transmitted disease. DATA SOURCES: A MEDLINE search was performed for all English citations from 1985 to 2000 that contain the keywords "Chlamydia trachomatis", "chlamydial infections", "risk factors" and "sex behaviour". All relevant references cited in articles that were obtained from the search were also included. DATA EXTRACTION: All articles obtained from the above sources were examined, and were included in the review if they met the following criteria: primary study examining sociodemographic or behavioural risk factors associated with genital chlamydial infection using multivariate analysis; study subjects 12 years of age and older; and study setting in a developed country. DATA SYNTHESIS AND CONCLUSIONS: Genital chlamydial infection has become the most commonly reported bacterial infection in North America over the past decade. Thirty-eight cross-sectional studies and six cohort studies were included in the present review. Most studies demonstrated that young men and women are at higher risk of being infected with chlamydia than older subjects. Chlamydia seems to be found in a diverse group of people, and unlike gonorrhea, is not concentrated in low income, minority core groups with high rates of partner change. However, a number of studies have shown that communities with well-established control programs are beginning to demonstrate this pattern. There is no clear evidence that chlamydia is associated with type of partners, contraceptive use, or age at first intercourse. Future research should follow this sexually transmitted disease as it evolves through the epidemiological stages to ensure that preventive and treatment services are reaching those people who are most likely to be infected

Sondeo de resultados adversos en las internaciones del Sistema Único de Salud

OBJETIVO: Descrever a frequência de rastreadores de potenciais resultados adversos em internações no Sistema Único de Saúde. MÉTODOS: Estudo retrospectivo, incluindo as internações de adultos na clínica médica (n = 3.565.811) e clínica cirúrgica (n = 2.614.048) no Brasil em 2007. O Sistema de Informações Hospitalares foi utilizado como fonte de informação. A mensuração dos resultados adversos baseou-se no rastreamento de 11 condições clínicas, definidas em estudos internacionais anteriores, registradas no campo diagnóstico secundário. Foram realizadas análises bivariada e multivariada, no intuito de associar resultado adverso, óbito (variável dependente) e outras variáveis como idade, utilização de unidade de terapia intensiva e realização de cirurgia. RESULTADOS: A frequência obtida foi 3,6 potenciais resultados adversos por 1.000 internações para ambas as clínicas, superior na clínica médica (5,3 por 1.000) em relação à clínica cirúrgica (1,3 por 1.000). Houve diferenças no perfil das internações: na clínica médica predominaram idosos, maior tempo médio de permanência, maior taxa de mortalidade e menor custo total de internação. O rastreador de resultado adverso mais frequente foi pneumonia hospitalar. Choque/parada cardíaca apresentou maior risco de óbito (OR = 5,76) em relação aos demais resultados adversos. Os maiores gastos com internações estiveram relacionados à sepse hospitalar. Os rastreadores de potencial resultado adverso apresentaram altas chances de óbito, mesmo com a introdução de variáveis como uso de terapia intensiva e realização de cirurgia. CONCLUSÕES: A alta frequência de resultados adversos em internações indica a necessidade de desenvolver estratégias de monitoramento e melhorias dirigidas para a segurança do paciente.OBJETIVO: Describir la frecuencia de sondeos de potenciales resultados adversos en internaciones en el Sistema Único de Salud. MÉTODOS: Estudio retrospectivo, incluyendo las internaciones de adultos en la clínica médica (n=3.565.811) y clínica quirúrgica (n=2.614.048) en Brasil en 2007. El Sistema de Informaciones Hospitalarias fue utilizado como fuente de información. La medición de los resultados adversos se basó en el sondeo de 11 condiciones clínicas, definidas en estudios internacionales anteriores, registradas en el campo diagnóstico secundario. Se realizaron análisis bivariado y multivariado, con el propósito de asociar resultado adverso, óbito (variable dependiente) y otras variables como edad, utilización de unidad de terapia intensiva y realización de cirugía. RESULTADOS: La frecuencia obtenida fue 3,6 potenciales resultados adversos por 1.000 internaciones para ambas clínicas, superior en la clínica médica (5,3 por 1.000) con relación a la clínica quirúrgica (1,3 por 1.000). Hubo diferencias en el perfil de las internaciones: en la clínica médica predominaron ancianos, mayor tiempo promedio de permanencia, mayor tasa de mortalidad y menor costo total de internación. El sondeo de resultado adverso más frecuente fue neumonía hospitalaria. Choque/parada cardíaca presentó mayor riesgo de óbito (OR= 5,76) con relación a los demás resultados adversos. Los mayores gastos con internaciones estuvieron relacionados con la asepsia hospitalaria. Los sondeos de potencial resultado adverso presentaron altas probabilidades de óbito aún con la introducción de variables como uso de terapia intensiva y realización de cirugía. CONCLUSIONES: La alta frecuencia de resultados adversos en internaciones muestran la necesidad de desarrollar estrategias de monitoreo y mejoras dirigidas a la seguridad del paciente.OBJECTIVE: To assess the frequency of screening for potential adverse outcomes in hospitalizations of the Brazilian Unified Health System. METHODS: A retrospective study, including all hospital admissions of adults in medical clinics (n = 3,565,811) and surgical clinics (n = 2,614,048) in Brazil in 2007. The Hospital Information System was used as a source of information. The measurement of adverse events was based on screening for eleven clinical conditions, as defined by previous international studies, recorded in the secondary diagnosis field. We performed bivariate and multivariate analysis to investigate associations between adverse events, death (dependent variable) and other variables such as age, use of the intensive care unit and performance of surgery. RESULTS: The frequency obtained for both clinic types was 3.6 potential adverse events per 1,000 admissions, with a greater frequency in medical clinics (5.3 per 1,000) than in surgery clinics (1.3 per 1,000). There were differences in the profile of hospital admissions between the two clinics: medical clinics were characterized by a predominance of older adults, longer average length of stay, higher mortality rate and lower total cost of hospitalization. The most common potential adverse outcome was hospital-acquired pneumonia. Cardiac arrest had a higher risk of death (OR= 5.76) compared to other potential adverse outcomes. Increased cost for hospitalizations was associated with sepsis. The conditions used as the screening criteria were associated with greater odds of death even after the introduction of variables such as use of intensive care and surgery. CONCLUSIONS: The high frequency of adverse outcomes in hospital admissions indicates a need to develop monitoring strategies and to improve quality of care for improved patient safety

Flat-brane Compactifications in Supergravity Induced by Scalars

We discuss flat compactifications of supergravities in diverse dimensions in the presence of branes. The compactification is induced by the scalar fields of supergravity and it is such that there is no relic cosmological constant on the brane, rendering this way the latter flat. We discuss in particular the D=4, $N=2,4$ and D=8, N=1 supergravities with $n=1,2,3$ vector multiplets where the scalar manifolds are Grassmannian cosets of the form $SO(2,n)/SO(2)\times SO(n)$. By introducing branes at certain points in the transverse space, finite energy solutions to the field equations are constructed. Some of the solutions we present may be interpreted as intersecting branes.Comment: 26 page