Calibrated Surfaces and Supersymmetric Wilson Loops

We study the dual gravity description of supersymmetric Wilson loops whose expectation value is unity. They are described by calibrated surfaces that end on the boundary of anti de-Sitter space and are pseudo-holomorphic with respect to an almost complex structure on an eight-dimensional slice of AdS_5 x S^5. The regularized area of these surfaces vanishes, in agreement with field theory non-renormalization theorems for the corresponding operators.Comment: 28 pages, 2 figure

Relationship between cortisol and physical performance in older persons

Objective: Hypercortisolism is associated with muscle weakness. This study examines the relationship between cortisol and physical performance in older persons. Design/patients: The study was conducted within the Longitudinal Aging Study Amsterdam (LASA), an ongoing cohort study in a population-based sample of healthy older persons in the Netherlands. Data from the second (1995/1996) and fourth (2001/2002) cycle were used pertaining to 1172 (65-88 years) and 884 (65-94 years) men and women, respectively. Measurements: Physical performance was measured by adding up scores on the chair stands, tandem stand and walk test (range 0-12). In the second cycle serum total and calculated free cortisol were assessed; in the fourth cycle evening salivary cortisol was assessed. Regression analysis (stratified for sex, adjusted for age, body mass index, alcohol use, physical activity and region) was performed to examine the cross-sectional relationship between cortisol and physical performance. Results: Women with higher calculated free cortisol scored less well on physical performance (b = -0.28 per SD higher cortisol, P = 0.016), which was mainly explained by poorer performance on the tandem stand (OR = 1.32 for a lower score per SD higher cortisol, P = 0.003). Men with higher salivary cortisol scored less well on physical performance (b = -0.90 in the highest vs. the lowest quartile, P = 0.008), which was mainly explained by poorer performance on the chair stands and walk test (OR = 1.88, P = 0.020 and OR = 1.81, P = 0.027, respectively, in the highest vs. the lowest quartile). Conclusion: Physical performance is negatively associated with high cortisol levels in older persons. © 2007 The Authors

Photons and Gravitons as Goldstone Bosons, and the Cosmological Constant

We reexamine a scenario in which photons and gravitons arise as Goldstone bosons associated with the spontaneous breaking of Lorentz invariance. We study the emergence of Lorentz invariant low energy physics in an effective field theory framework, with non-Lorentz invariant effects arising from radiative corrections and higher order interactions. Spontaneous breaking of the Lorentz group also leads to additional exotic but weakly coupled Goldstone bosons, whose dispersion relations we compute. The usual cosmological constant problem is absent in this context: being a Goldstone boson, the graviton can never develop a potential, and the existence of a flat spacetime solution to the field equations is guaranteed.Comment: 21 pages, harvma

Open Wilson Lines and Group Theory of Noncommutative Yang-Mills Theory in Two Dimensions

The correlation functions of open Wilson line operators in two-dimensional Yang-Mills theory on the noncommutative torus are computed exactly. The correlators are expressed in two equivalent forms. An instanton expansion involves only topological numbers of Heisenberg modules and enables extraction of the weak-coupling limit of the gauge theory. A dual algebraic expansion involves only group theoretic quantities, winding numbers and translational zero modes, and enables analysis of the strong-coupling limit of the gauge theory and the high-momentum behaviour of open Wilson lines. The dual expressions can be interpreted physically as exact sums over contributions from virtual electric dipole quanta.Comment: 37 pages. References adde

Properties of Chiral Wilson Loops

We study a class of Wilson Loops in N =4, D=4 Yang-Mills theory belonging to the chiral ring of a N=2, d=1 subalgebra. We show that the expectation value of these loops is independent of their shape. Using properties of the chiral ring, we also show that the expectation value is identically 1. We find the same result for chiral loops in maximally supersymmetric Yang-Mills theory in three, five and six dimensions. In seven dimensions, a generalized Konishi anomaly gives an equation for chiral loops which closely resembles the loop equations of the three dimensional Chern-Simons theory.Comment: 15 pages, two pictures, some references adde