544 research outputs found
Chronology protection in stationary three-dimensional spacetimes
We study chronology protection in stationary, rotationally symmetric
spacetimes in 2+1 dimensional gravity, focusing especially on the case of
negative cosmological constant. We show that in such spacetimes closed timelike
curves must either exist all the way to the boundary or, alternatively, the
matter stress tensor must violate the null energy condition in the bulk. We
also show that the matter in the closed timelike curve region gives a negative
contribution to the conformal weight from the point of view of the dual
conformal field theory. We illustrate these properties in a class of examples
involving rotating dust in anti-de Sitter space, and comment on the use of the
AdS/CFT correspondence to study chronology protection.Comment: 20 pages. V2: minor corrections, Outlook expanded, references added,
published versio
New Sum Rules from Low Energy Compton Scattering on Arbitrary Spin Target
We derive two sum rules by studying the low energy Compton scattering on a
target of arbitrary (nonzero) spin j. In the first sum rule, we consider the
possibility that the intermediate state in the scattering can have spin |j \pm
1| and the same mass as the target. The second sum rule applies if the theory
at hand possesses intermediate narrow resonances with masses different from the
mass of the scatterer. These sum rules are generalizations of the
Gerasimov-Drell-Hearn-Weinberg sum rule. Along with the requirement of tree
level unitarity, they relate different low energy couplings in the theory.
Using these sum rules, we show that in certain cases the gyromagnetic ratio can
differ from the "natural" value g=2, even at tree level, without spoiling
perturbative unitarity. These sum rules can be used as constraints applicable
to all supergravity and higher-spin theories that contain particles charged
under some U(1) gauge field. In particular, applied to four dimensional N=8
supergravity in a spontaneously broken phase, these sum rules suggest that for
the theory to have a good ultraviolet behavior, additional massive states need
to be present, such as those coming from the embedding of the N=8 supergravity
in type II superstring theory. We also discuss the possible implications of the
sum rules for QCD in the large-N_c limit.Comment: 18 pages, v2: discussion on black hole contribution is included,
references added; v3: extended discussion in introduction, version to appear
in JHE
The Hubble Constant from Observations of the Brightest Red Giant Stars in a Virgo-Cluster Galaxy
The Virgo and Fornax clusters of galaxies play central roles in determining
the Hubble constant H_0. A powerful and direct way of establishing distances
for elliptical galaxies is to use the luminosities of the brightest red-giant
stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct
observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo
cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we
estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a
low-density Universe with the simplest cosmology, the age of the Universe is no
more than 12-13 billion years.Comment: 12 pages, LaTeX, with 2 postscript figures; in press for Nature, July
199
Comparing the frequency of common genetic variants and haplotypes between carriers and non-carriers of BRCA1 and BRCA2 deleterious mutations in Australian women diagnosed with breast cancer before 40 years of age
BACKGROUND: BRCA1 and BRCA2 mutations are found in a proportion of families with multiple early-onset breast cancers. There are a large number of different deleterious mutations in both genes, none of which would be detectable using standard genetic association studies. Single common variants and haplotypes of common variants may capture groups of deleterious mutations since some low prevalence haplotypes of common variants occur more frequently among chromosomes that carry rare, deleterious mutations than chromosomes that do not. METHODS: DNA sequence data for BRCA1 and BRCA2 was obtained from 571 participants from the Australian Breast Cancer Family Study. Genetic variants were classified as either deleterious mutations or common genetic variants. Variants tagging common polymorphisms were selected and haplotypes resolved using Haploview. Their frequency was compared to those with and without deleterious mutations using a permutation test. RESULTS: A common genetic variant in BRCA1 (3232A > G) was found to be over-represented in deleterious mutation carriers (p = 0.05), whereas a common genetic variant in BRCA2 (1342A > C) occurred less frequently in deleterious mutation carriers (p = 0.04). All four of the common BRCA1 variants used to form haplotypes occurred more frequently in the deleterious mutation carriers when compared to the non-carriers, but there was no evidence of a difference in the distributions between the two groups (p = 0.34). In BRCA2, all four common variants were found to occur less frequently in the deleterious mutation carriers when compared to non-carriers, but the evidence for difference in the distribution between the two groups was weak (p = 0.16). Several less common haplotypes of common BRCA1 variants were found to be over-represented among deleterious mutation carriers but there was no evidence for this at the population level. In BRCA2, only the most common haplotype was found to occur more frequently in deleterious mutation carriers, with again no evidence at the population level. CONCLUSIONS: We observed differences in the frequency of common genetic variants of the BRCA1 and BRCA2 and their haplotypes between early-onset breast cancer cases who did and did not carry deleterious mutations in these genes. Although our data provide only weak evidence for a difference in frequencies at the population level, the number of deleterious mutation carriers was low and the results may yet be substantiated in a larger study using pooled data
End-stage renal disease in young black males in a black-white population: longitudinal analysis of the Bogalusa Heart Study
<p>Abstract</p> <p>Background</p> <p>Risk factors in childhood create a life-long burden important in the development of cardiovascular (CV) disease in adulthood. Many risk factors for CV disease (e.g., hypertension) also increase the risk of renal disease. However, the importance of childhood risk factors on the development of chronic kidney disease and end-stage renal disease (ESRD) is not well characterized.</p> <p>Methods</p> <p>The current observations include data from Bogalusa Heart Study participants who were examined multiple times as children between 1973 and 1988.</p> <p>Results</p> <p>Through 2006, fifteen study participants subsequently developed ESRD in adulthood; seven with no known overt cause. Although the Bogalusa Heart Study population is 63% white and 37% black and 51% male and 49% female, all seven ESRD cases with no known overt cause were black males (p < 0.001). Mean age-adjusted systolic and diastolic blood pressure in childhood was higher among the ESRD cases (114.5 mmHg and 70.1 mmHg, respectively) compared to black (103.0 mmHg and 62.3 mmHg, respectively) and white (mean = 103.3 mmHg and 62.3 mmHg, respectively) boys who didn't develop ESRD. The mean age-adjusted body mass index in childhood was 23.5 kg/m<sup>2 </sup>among ESRD cases and 18.6 kg/m<sup>2 </sup>and 18.9 kg/m<sup>2 </sup>among black and white boys who didn't develop ESRD, respectively. Plasma glucose in childhood was not significantly associated with ESRD.</p> <p>Conclusion</p> <p>These data suggest black males have an increased risk of ESRD in young adulthood. Elevated body mass index and blood pressure in childhood may increase the risk for developing ESRD as young adults.</p
A frequentist framework of inductive reasoning
Reacting against the limitation of statistics to decision procedures, R. A.
Fisher proposed for inductive reasoning the use of the fiducial distribution, a
parameter-space distribution of epistemological probability transferred
directly from limiting relative frequencies rather than computed according to
the Bayes update rule. The proposal is developed as follows using the
confidence measure of a scalar parameter of interest. (With the restriction to
one-dimensional parameter space, a confidence measure is essentially a fiducial
probability distribution free of complications involving ancillary statistics.)
A betting game establishes a sense in which confidence measures are the only
reliable inferential probability distributions. The equality between the
probabilities encoded in a confidence measure and the coverage rates of the
corresponding confidence intervals ensures that the measure's rule for
assigning confidence levels to hypotheses is uniquely minimax in the game.
Although a confidence measure can be computed without any prior distribution,
previous knowledge can be incorporated into confidence-based reasoning. To
adjust a p-value or confidence interval for prior information, the confidence
measure from the observed data can be combined with one or more independent
confidence measures representing previous agent opinion. (The former confidence
measure may correspond to a posterior distribution with frequentist matching of
coverage probabilities.) The representation of subjective knowledge in terms of
confidence measures rather than prior probability distributions preserves
approximate frequentist validity.Comment: major revisio
Effectiveness of an online curriculum for medical students on genetics, genetic testing and counseling
Background: It is increasingly important that physicians have a thorough understanding of the basic science of human genetics and the ethical, legal and social implications (ELSI) associated with genetic testing and counseling. Methods: The authors developed a series of web-based courses for medical students on these topics. The course modules are interactive, emphasize clinical case studies, and can easily be incorporated into existing medical school curricula. Results: Results of a ‘real world’ effectiveness trial indicate that the courses have a statistically significant effect on knowledge, attitude, intended behavior and self-efficacy related to genetic testing (p<0.001; N varies between 163 and 596 for each course). Conclusions: The results indicate that this curriculum is an effective tool for educating medical students on the ELSI associated with genetic testing and for promoting positive changes in students' confidence, counseling attitudes and behaviors
Family and Early Life Factors Associated With Changes in Overweight Status Between Ages 5 and 14 Years: Findings From The Mater University Study Of Pregnancy and its Outcomes
Objective To describe different patterns of overweight status between ages 5 and 14 y and examine the role of modifiable family and early life characteristics in explaining different patterns of change between these two ages. Design A population-based prospective birth cohort. Subjects A total of 2934 children (52% males) who were participants in the Mater-University study of pregnancy, Brisbane, and who were examined at ages 5 and 14 y. Main outcome measures Four patterns of change in overweight/obesity status between ages 5 and 14 y: (i) normal at both ages; (ii) normal at 5 y and overweight/obese at 14 y; (iii) overweight/obese at 5 y and normal at 14 y; (iv) overweight/obese at both ages. Results Of the 2934 participants, 2018 (68.8%) had a normal body mass index (BMI) at ages 5 and 14 y, 425 (14.5%) changed from a normal BMI at age 5 y to overweight or obese at age 14 y, 175 (6.0%) changed from being overweight or obese at age 5 y to normal weight at age 14 y and 316 (10.8%) were overweight or obese at both ages 5 and 14 y. Girls were more likely to make the transition from overweight or obese at age 5 y to normal at 14 y than their boy counterparts. Children whose parents were overweight or obese were more likely to change from having a normal BMI at age 5 y to being overweight at 14 y (fully adjusted RR: 6.17 (95% CI: 3.97, 9.59)) and were more likely to be overweight at both ages (7.44 (95% CI: 4.60, 12.02)). Birth weight and increase in weight over the first 6 months of life were both positively associated with being overweight at both ages. Other explanatory factors were not associated with the different overweight status transitions. Conclusions Parental overweight status is an important determinant of whether a child is overweight at either stage or changes from being not overweight at 5 y to becoming so at 14 y
Physics of Neutron Star Crusts
The physics of neutron star crusts is vast, involving many different research
fields, from nuclear and condensed matter physics to general relativity. This
review summarizes the progress, which has been achieved over the last few
years, in modeling neutron star crusts, both at the microscopic and macroscopic
levels. The confrontation of these theoretical models with observations is also
briefly discussed.Comment: 182 pages, published version available at
<http://www.livingreviews.org/lrr-2008-10
A goldstino at the bottom of the cascade
Working within a five-dimensional consistent truncation of type IIB
supergravity dimensionally reduced on , we consider supersymmetry
breaking solutions with the asymptotics of the supersymmetric
Klebanov-Strassler background. There exists a two-parameter family of such
solutions. Within this family, we show that those (and only those) solutions
related to antiD-branes at the tip of the conifold correspond to dual field
theory vacua where a goldstino mode is present and supercurrent Ward identities
hold. Our findings do not depend on the IR singularity of the dual backgrounds,
nor on its resolution. As such, they constitute an independent, necessary check
for the existence of supersymmetry breaking vacua in the conifold cascading
gauge theory. Our analysis relies on a holographic derivation of the Ward
identities which has a wider applicability, beyond the specific system and
symmetries considered here.Comment: 33+1 pages; v2: Slight rephrasing of the abstract, typos corrected
and a reference added; v3: More minor typos corrected, footnote 18 added,
version published in JHE
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