Dispersion corrections to parity violating electron scattering

We consider the dispersion correction to elastic parity violating electron-proton scattering due to \gammaZ exchange. In a recent publication, this correction was reported to be substantially larger than the previous estimates. In this paper, we study the dispersion correction in greater detail. We confirm the size of the disperion correction to be 6% for the QWEAK experiment designed to measure the proton weak charge. We enumerate parameters that have to be constrained to better than relative 30% in order to keep the theoretical uncertainty for QWEAK under control.Comment: 6 pages, 3 figures, 2 tables; To be published in the proceedings of the VIII Latin American Symposium on Nuclear Physics and Applications, December 15-19, 2009, Santiago, Chiil

Where is the Information Stored in Black Holes?

It is shown that many modes of the gravitational field exist only inside the horizon of an extreme black hole in string theory. At least in certain cases, the number of such modes is sufficient to account for the Bekenstein-Hawking entropy. These modes are associated with sources which carry Ramond-Ramond charge, and so may be viewed as the strong coupling limit of D-branes. Although these sources naturally live at the singularity, they are well defined and generate modes which extend out to the horizon. This suggests that the information in an extreme black hole is not localized near the singularity or the horizon, but extends between them.Comment: 21 pages, reference corrected and comment adde

Position-dependent exact-exchange energy for slabs and semi-infinite jellium

The position-dependent exact-exchange energy per particle $\varepsilon_x(z)$ (defined as the interaction between a given electron at $z$ and its exact-exchange hole) at metal surfaces is investigated, by using either jellium slabs or the semi-infinite (SI) jellium model. For jellium slabs, we prove analytically and numerically that in the vacuum region far away from the surface $\varepsilon_{x}^{\text{Slab}}(z \to \infty) \to - e^{2}/2z$, {\it independent} of the bulk electron density, which is exactly half the corresponding exact-exchange potential $V_{x}(z \to \infty) \to - e^2/z$ [Phys. Rev. Lett. {\bf 97}, 026802 (2006)] of density-functional theory, as occurs in the case of finite systems. The fitting of $\varepsilon_{x}^{\text{Slab}}(z)$ to a physically motivated image-like expression is feasible, but the resulting location of the image plane shows strong finite-size oscillations every time a slab discrete energy level becomes occupied. For a semi-infinite jellium, the asymptotic behavior of $\varepsilon_{x}^{\text{SI}}(z)$ is somehow different. As in the case of jellium slabs $\varepsilon_{x}^{\text{SI}}(z \to \infty)$ has an image-like behavior of the form $\propto - e^2/z$, but now with a density-dependent coefficient that in general differs from the slab universal coefficient 1/2. Our numerical estimates for this coefficient agree with two previous analytical estimates for the same. For an arbitrary finite thickness of a jellium slab, we find that the asymptotic limits of $\varepsilon_{x}^{\text{Slab}}(z)$ and $\varepsilon_{x}^{\text{SI}}(z)$ only coincide in the low-density limit ($r_s \to \infty$), where the density-dependent coefficient of the semi-infinite jellium approaches the slab {\it universal} coefficient 1/2.Comment: 26 pages, 7 figures, to appear in Phys. Rev.

Lipase inhibition attenuates the acute inhibitory effects of oral fat on food intake in healthy subjects

The lipase inhibitor, orlistat, is used in the treatment of obesity and reduces fat absorption by about 30%. However, the mean weight loss induced by orlistat is less than expected for the degree of fat malabsorption. It was hypothesised that lipase inhibition with orlistat attenuates the suppressive effects of oral fat on subsequent energy intake in normal-weight subjects. Fourteen healthy, lean subjects (nine males, five females; aged 25 +/- 1.3 years) were studied twice, in a double-blind fashion. The subjects received a high-fat yoghurt 'preload' (males 400 g (2562 kJ); females 300 g (1923 kJ)), containing orlistat (120 mg) on one study day (and no orlistat on the other 'control' day), 30 min before ad libitum access to food and drinks; energy intake was assessed during the following 8 h. Blood samples were taken at regular intervals for the measurement of plasma cholecystokinin (CCK). Each subject performed a 3 d faecal fat collection following each study. Energy intake during the day was greater following orlistat (10,220 (SEM 928) kJ) v. control (9405 (SEM 824) kJ) (P=0.02). On both days plasma CCK increased (P<0.05) after the preload. Plasma CCK 20 min following ingestion of the preload was less after orlistat (4.1 (SEM 0.9) pmol/l) v. control (5.3 (SEM 0.9) pmol/l (P=0.028); however there was no difference in the area under the curve 0-510 min between the two study days. Fat excretion was greater following orlistat (1017 (SEM 168) kJ) v. control (484 (SEM 90) kJ) (P=0.004). In conclusion, in healthy, lean subjects the acute inhibitory effect of fat on subsequent energy intake is attenuated by orlistat and the increase in energy intake approximates the energy lost due to fat malabsorption.Deirdre O’Donovan, Christine Feinle-Bisset, Judith Wishart and Michael Horowit

Interacting Intersections

Intersecting p-branes can be viewed as higher-dimensional interpretations of multi-charge extremal p-branes, where some of the individual p-branes undergo diagonal dimensional oxidation, while the others oxidise vertically. Although the naive vertical oxidation of a single p-brane gives a continuum of p-branes, a more natural description arises if one considers a periodic array of p-branes in the higher dimension, implying a dependence on the compactification coordinates. This still reduces to the single lower-dimensional p-brane when viewed at distances large compared with the period. Applying the same logic to the multi-charge solutions, we are led to consider more general classes of intersecting p-brane solutions, again depending on the compactification coordinates, which turn out to be described by interacting functions rather than independent harmonic functions. These new solutions also provide a more satisfactory interpretation for the lower-dimensional multi-charge p-branes, which otherwise appear to be nothing more than the improbable coincidence of charge-centres of individual constituents with zero binding energy.Comment: 20 pages, Latex, references adde

Comments on Black Holes in String Theory

A very brief review is given of some of the developments leading to our current understanding of black holes in string theory. This is followed by a discussion of two possible misconceptions in this subject - one involving the stability of small black holes and the other involving scale radius duality. Finally, I describe some recent results concerning quasinormal modes of black holes in anti de Sitter spacetime, and their implications for strongly coupled conformal field theories (in various dimensions).Comment: 13 pages. Talk given at Strings '99, Potsdam, German