From correlation functions to Wilson loops

We start with an n-point correlation function in a conformal gauge theory. We show that a special limit produces a polygonal Wilson loop with $n$ sides. The limit takes the $n$ points towards the vertices of a null polygonal Wilson loop such that successive distances $x^2_{i,i+1} \to 0$. This produces a fast moving particle that generates a "frame" for the Wilson loop. We explain in detail how the limit is approached, including some subtle effects from the propagation of a fast moving particle in the full interacting theory. We perform perturbative checks by doing explicit computations in N=4 super-Yang-Mills.Comment: 37 pages, 10 figures; typos corrected, references adde

The utility of B-type natriuretic peptide in predicting postoperative cardiac events and mortality in patients undergoing major emergency non-cardiac surgery

B-type natriuretic peptide (BNP) levels predict cardiovascular risk in several settings. We hypothesized that they would identify individuals at increased risk of complications and mortality following major emergency non-cardiac surgery.Forty patients were studied with a primary end-point of a new post-operative cardiac event, and/or development of significant ECG changes, and/or cardiac death. The main secondary outcome was all cause mortality at 6 months. Preoperative BNP levels were higher in 11 patients who suffered a new postoperative cardiac event (p=0.001) and predicted this outcome with an area under the receiver operating characteristic curve of 0.85 (CI=0.72-0.98,p=0.001). A pre-operative BNP value >170pg.ml-1 has a sensitivity of 82% and a specificity of 79% for the primary end-point. In this small study, pre-operative BNP levels identify patients undergoing major emergency non-cardiac surgery who are at increased risk of early post-operative cardiac events. Larger studies are required to confirm these data.Peer reviewedPreprin

Medical students’ use of caffeine for ‘academic purposes’ and their knowledge of its benefits, side-effects and withdrawal symptoms

Background: Caffeine is often used for its benefits, which include increased vigilance. It does have side-effects, however, such as palpitations andwithdrawal symptoms that include headaches and drowsiness. Tertiary education often requires students to study for extended hours, especiallyduring periods of increased workload prior to tests and examinations. Medical students, who have to master a very large volume of academic work ina limited period of time, are no exception. This cross-sectional study investigated caffeine use for ‘academic purposes’ by first- to third-year medicalstudents at the University of the Free State in 2006, and their knowledge of its benefits, side-effects and withdrawal symptoms.Methods: Data were collected by means of an anonymous, self-administered questionnaire that was completed by students during formal classtime, arranged in advance with the relevant lecturers. Questionnaires were available in Afrikaans and English. A pilot study was conducted on20 physiotherapy students to test the questionnaire. Chi-squared and Kruskall-Wallis tests were used to compare categorical and numerical variables,respectively. Ethical approval to perform the investigation was granted by the Ethics Committee of the Faculty of Health Sciences, University of theFree State.Results: A 90.5% (360/389) response rate was obtained. Ninety-four per cent of participants used caffeine, with academic purposes (62.6%) amongthe three most frequent reasons given for its consumption. Other reasons included social consumption (70%) and preference for the taste (72.4%).Coffee (88.2%) was the most commonly consumed caffeinated product among these students, followed by energy mixtures and tablets (37.9%),and soft drinks (36%). Third-year students were the heaviest consumers of coffee for academic purposes. An increase in caffeine consumptionfor academic purpose was directly related to progression from first- to third- year of the medical course. The average scores for questions on thebenefits, side-effects and withdrawal symptoms were all below 1.5 out of 5. Misconceptions about caffeine were also identified. With regard to thebenefits of caffeine, the most commonly cited misconception was that it could be used as a substitute for sleep (26.7% of respondents). The mostcommon misconception regarding its side-effects was that it caused hot flushes (21.9%), while aggression (27.2%) was cited as the most commonmisconception regarding caffeine withdrawal.Conclusions: The high percentage of caffeine usage and low scores in the caffeine knowledge test indicated that most participants were usingcaffeine without having sufficient knowledge of its benefits, side-effects and withdrawal symptoms. It is recommended that awareness programmeson the side-effects and symptoms of caffeine withdrawal should be implemented by the student health and counselling facilities on campus. Thedisplay of posters in strategic venues and distribution of pamphlets could assist in the dissemination of information on this extensively consumedsubstance

Renormalisation of heavy-light light ray operators

We calculate the renormalisation of different light ray operators with one light degree of freedom and a static heavy quark. Both $2\to2$- and $2\to3$-kernels are considered. A comparison with the light-light case suggests that the mixing with three-particle operators is solely governed by the light degrees of freedom. Additionally we show that conformal symmetry is already broken at the level of the one loop counterterms due to the additional UV-renormalisation of a cusp in the two contributing Wilson-lines. This general feature can be used to fix the $2\to2$-renormalisation kernels up to a constant. Some examples for applications of our results are given.Comment: 23 pages, 5 figures; v2: changed some wording, added a few references and one appendix concerning some subtleties related to gauge fixing and ghost terms; v3: clarified calculation in section 3.2., added an explicit calculation in section 5.2, corrected a few typos and one figure, added a few comments, results unchanged, except for typesetting matches version to appear in JHE

Integration of Visual Information in Auditory Cortex Promotes Auditory Scene Analysis through Multisensory Binding

How and where in the brain audio-visual signals are bound to create multimodal objects remains unknown. One hypothesis is that temporal coherence between dynamic multisensory signals provides a mechanism for binding stimulus features across sensory modalities. Here, we report that when the luminance of a visual stimulus is temporally coherent with the amplitude fluctuations of one sound in a mixture, the representation of that sound is enhanced in auditory cortex. Critically, this enhancement extends to include both binding and non-binding features of the sound. We demonstrate that visual information conveyed from visual cortex via the phase of the local field potential is combined with auditory information within auditory cortex. These data provide evidence that early cross-sensory binding provides a bottom-up mechanism for the formation of cross-sensory objects and that one role for multisensory binding in auditory cortex is to support auditory scene analysis

Eikonal methods applied to gravitational scattering amplitudes

We apply factorization and eikonal methods from gauge theories to scattering amplitudes in gravity. We hypothesize that these amplitudes factor into an IR-divergent soft function and an IR-finite hard function, with the former given by the expectation value of a product of gravitational Wilson line operators. Using this approach, we show that the IR-divergent part of the n-graviton scattering amplitude is given by the exponential of the one-loop IR divergence, as originally discovered by Weinberg, with no additional subleading IR-divergent contributions in dimensional regularization.Comment: 16 pages, 3 figures; v2: title change and minor rewording (published version); v3: typos corrected in eqs.(3.2),(4.1

Two-Loop Soft Corrections and Resummation of the Thrust Distribution in the Dijet Region

The thrust distribution in electron-positron annihilation is a classical precision QCD observable. Using renormalization group (RG) evolution in Laplace space, we perform the resummation of logarithmically enhanced corrections in the dijet limit, $T\to 1$ to next-to-next-to-leading logarithmic (NNLL) accuracy. We independently derive the two-loop soft function for the thrust distribution and extract an analytical expression for the NNLL resummation coefficient $g_3$. To combine the resummed expressions with the fixed-order results, we derive the $\log(R)$-matching and $R$-matching of the NNLL approximation to the fixed-order NNLO distribution.Comment: 50 pages, 12 figures, 1 table. Few minor changes. Version accepted for publication in JHE