NEURO-PSYCHIATRIC DISORDERS IN THE BANTU

Click on the link to view

Higher-order gravity and the cosmological background of gravitational waves

The cosmological background of gravitational waves can be tuned by the higher-order corrections to the gravitational Lagrangian. In particular, it can be shown that assuming $R^{1+\epsilon}$, where $\epsilon$ indicates a generic (eventually small) correction to the Hilbert-Einstein action in the Ricci scalar $R$, gives a parametric approach to control the evolution and the production mechanism of gravitational waves in the early Universe.Comment: 6 pages, 8 figure

Future Boundary Conditions in De Sitter Space

We consider asymptotically future de Sitter spacetimes endowed with an eternal observatory. In the conventional descriptions, the conformal metric at the future boundary I^+ is deformed by the flux of gravitational radiation. We however impose an unconventional future "Dirichlet" boundary condition requiring that the conformal metric is flat everywhere except at the conformal point where the observatory arrives at I^+. This boundary condition violates conventional causality, but we argue the causality violations cannot be detected by any experiment in the observatory. We show that the bulk-to-bulk two-point functions obeying this future boundary condition are not realizable as operator correlation functions in any de Sitter invariant vacuum, but they do agree with those obtained by double analytic continuation from anti-de Sitter space.Comment: 16 page

Putting the genome on the map

The maps of our everyday lives are much more than just linear lists of place names. Instead, their colours, symbols, contours and grid lines seek to describe different types of landscape, and to depict the spatial relationships between structural and functional landmarks of the environment (Fig. 1). It was the combination of photography and aviation that revolutionized mapmaking in the early part of this century. In much the same way, it is fluorescence microscopy and digital imaging (Box 1) in combination with molecular genetics that is driving our emerging view of the genome in space and time

Conformal Transformations in Cosmology of Modified Gravity: the Covariant Approach Perspective

The 1+3 covariant approach and the covariant gauge-invariant approach to perturbations are used to analyze in depth conformal transformations in cosmology. Such techniques allow us to obtain very interesting insights on the physical content of these transformations, when applied to non-standard gravity. The results obtained lead to a number of general conclusions on the change of some key quantities describing any two conformally related cosmological models. In particular, it is shown that the physics in the Einstein frame has characteristics which are completely different from those in the Jordan frame. Even if some of the geometrical properties of the cosmology are preserved (homogeneous and isotropic Universes are mapped into homogeneous and isotropic universes), it can happen that decelerating cosmologies are mapped into accelerated ones. Differences become even more pronounced when first-order perturbations are considered: from the 1+3 equations it is seen that first-order vector and tensor perturbations are left unchanged in their structure by the conformal transformation, but this cannot be said of the scalar perturbations, which include the matter density fluctuations. Behavior in the two frames of the growth rate, as well as other evolutionary features, like the presence or absence of oscillations, etc., appear to be different too. The results obtained are then explicitly interpreted and verified with the help of some clarifying examples based on $f(R)$-gravity cosmologies.Comment: 26 pages, 8 figure

Complete constraints on a nonminimally coupled chaotic inflationary scenario from the cosmic microwave background

We present complete constraints imposed from observations of the cosmic microwave background radiation (CMBR) on the chaotic inflationary scenario with a nonminimally coupled inflaton field proposed by Fakir and Unruh (FU). Our constraints are complete in the sense that we investigate both the scalar density perturbation and the tensor gravitational wave in the Jordan frame, as well as in the Einstein frame. This makes the constraints extremely strong without any ambiguities due to the choice of frames. We find that the FU scenario generates tiny tensor contributions to the CMBR relative to chaotic models in minimal coupling theory, in spite of its spectral index of scalar perturbation being slightly tilted. This means that the FU scenario will be excluded if any tensor contributions to CMBR are detected by the forthcoming satellite missions. Conversely, if no tensor nature is detected despite the tilted spectrum, a minimal chaotic scenario will be hard to explain and the FU scenario will be supported.Comment: 7 pages, no figure, RevTeX, to appear in Phys.Rev. D59 (Mar. 15, 1999

Exchange Rates and Trade Balance Adjustment: A Multi-Country Empirical Analysis

This study assesses the response of the trade balance to exchange rate fluctuations across a large number of countries. Fixed-effects regressions are estimated for three country groups (industrial, developing and emerging markets) on annual data for 87 countries from 1994 to 2010. The trade balance improves significantly after a real depreciation, and to a similar degree, in the long run for all countries, but the adjustment is significantly slower for industrial countries. Emerging markets and developing countries display relatively fast adjustment. Disaggregation into exports and imports shows that the delayed adjustment in industrial countries is almost entirely on the export side. The rate of adjustment in emerging markets is slowing over time, consistent with their eventual graduation to high-income status. The ratio of trade to GDP is also highly sensitive to the real effective exchange rate, with a real depreciation of 10 % raising the trade/GDP ratio across the sample by approximately 4 %. This result, which presumably reflects movements in the prices of tradables relative to non-tradables, raises questions about the widespread use of the trade/GDP ratio as a trade policy indicator, without adjustment for real exchange rate effects

Experimental determination of the complete spin structure for anti-proton + proton -> anti-\Lambda + \Lambda at anti-proton beam momentum of 1.637 GeV/c

The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton + \pi^+ + proton + \pi^- has been measured with high statistics at anti-proton beam momentum of 1.637 GeV/c. The use of a transversely-polarized frozen-spin target combined with the self-analyzing property of \Lambda/anti-\Lambda decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of eleven real parameters for each bin of scattering angle, each of these parameters is determined with reasonable precision. From these results all conceivable spin-correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy. Existing theoretical models do not give good predictions for those spin-observables that had not been previously measured.Comment: To be published in Phys. Rev. C. Tables of results (i.e. Ref. 24) are available at http://www-meg.phys.cmu.edu/~bquinn/ps185_pub/results.tab 24 pages, 16 figure