Decaying Dark Energy in Higher-Dimensional Gravity

We use data from observational cosmology to put constraints on higher-dimensional extensions of general relativity in which the effective four-dimensional dark-energy density (or cosmological "constant") decays with time. In particular we study the implications of this decaying dark energy for the age of the universe, large-scale structure formation, big-bang nucleosynthesis and the magnitude-redshift relation for Type Ia supernovae. Two of these tests (age and the magnitude-redshift relation) place modest lower limits on the free parameter of the theory, a cosmological length scale L akin to the de Sitter radius. These limits will improve if experimental uncertainties on supernova magnitudes can be reduced around z=1.Comment: 11 pages, 5 figures, submitted to A&

Scaling Relations for the Cosmological "Constant" in Five-Dimensional Relativity

When the cosmological "constant" is derived from modern five-dimensional relativity, exact solutions imply that for small systems it scales in proportion to the square of the mass. However, a duality transformation implies that for large systems it scales as the inverse square of the mass

Astrophysical Implications of Higher-Dimensional Gravity

We review the implications of modern higher-dimensional theories of gravity for astrophysics and cosmology. In particular, we discuss the latest developments of space-time-matter theory in connection with dark matter, particle dynamics and the cosmological constant, as well as related aspects of quantum theory. There are also more immediate tests of extra dimensions, notably involving perturbations of the cosmic 3K microwave background and the precession of a supercooled gyroscope in Earth orbit. We also outline some general features of embeddings, and include pictures of the big bang as viewed from a higher dimension.Comment: 23 pages, 2 figures; to appear in Space Science Reviews; v3: typos corrected and minor changes to text, expanded derivation of fundamental mode adde

Dark Matter and Background Light

Progress in observational cosmology over the past five years has established that the Universe is dominated dynamically by dark matter and dark energy. Both these new and apparently independent forms of matter-energy have properties that are inconsistent with anything in the existing standard model of particle physics, and it appears that the latter must be extended. We review what is known about dark matter and energy from their impact on the light of the night sky. Most of the candidates that have been proposed so far are not perfectly black, but decay into or otherwise interact with photons in characteristic ways that can be accurately modelled and compared with observational data. We show how experimental limits on the intensity of cosmic background radiation in the microwave, infrared, optical, ultraviolet, x-ray and gamma-ray bands put strong limits on decaying vacuum energy, light axions, neutrinos, unstable weakly-interacting massive particles (WIMPs) and objects like black holes. Our conclusion is that the dark matter is most likely to be WIMPs if conventional cosmology holds; or higher-dimensional sources if spacetime needs to be extended.Comment: 185 pages, 42 figures, to appear in Physics Report

Waves and causality in higher dimensions

We give a new, wave-like solution of the field equations of five-dimensional relativity. In ordinary three-dimensional space, the waves resemble de Broglie or matter waves, whose puzzling behaviour can be better understood in terms of one or more extra dimensions. Causality is appropriately defined by a null higher-dimensional interval. It may be possible to test the properties of these waves in the laboratory.Comment: 15 pages, no figure