Article
Acceleration of the Universe, String Theory and a Varying Speed of Light
06/2001;
Source: arXiv

Article: New varying speed of light theories
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ABSTRACT: We review recent work on the possibility of a varying speed of light (VSL). We start by discussing the physical meaning of a varying $c$, dispelling the myth that the constancy of $c$ is a matter of logical consistency. We then summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz invariance; bimetric theories (where the speeds of gravity and light are not the same); locally Lorentz invariant VSL theories; theories exhibiting a color dependent speed of light; varying $c$ induced by extra dimensions (e.g. in the braneworld scenario); and field theories where VSL results from vacuum polarization or CPT violation. We show how VSL scenarios may solve the cosmological problems usually tackled by inflation, and also how they may produce a scaleinvariant spectrum of Gaussian fluctuations, capable of explaining the WMAP data. We then review the connection between VSL and theories of quantum gravity, showing how ``doubly special'' relativity has emerged as a VSL effective model of quantum spacetime, with observational implications for ultra high energy cosmic rays and gamma ray bursts. Some recent work on the physics of ``black'' holes and other compact objects in VSL theories is also described, highlighting phenomena associated with spatial (as opposed to temporal) variations in $c$. Finally we describe the observational status of the theory. The evidence is currently slim  redshift dependence in the atomic fine structure, anomalies with ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data. The constraints (e.g. those arising from nucleosynthesis or geological bounds) are tight, but not insurmountable. We conclude with the observational predictions of the theory, and the prospects for its refutation or vindication.Reports on Progress in Physics 06/2003; · 13.23 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Dbranes are by now an integral part of our toolbox towards understanding nature. In this review, we will describe recent progress in their use to realize fundamental interactions. The realization of the standard model and relevant physics and problems will be detailed. New ideas on realizing fourdimensional gravity use the brane idea in an important way. Such approaches will be reviewed and compared to the standard paradigm of compactification. Branes can play a pivotal role both in early and lateuniverse cosmology mainly via the braneuniverse paradigm. Brane realizations of various cosmological ideas (early inflation, sources for dark matter and dark energy, massive gravity, etc)are also reviewed.Physics Reports 12/2005; · 22.93 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: This is a review of aspects of Dbrane applications to particle physics and cosmology. Dbranes provide interesting alternatives to standard unification of interactions. Moreover they entail new mechanisms in cosmology that have the potential to explain recent observational data.Fortschritte der Physik 01/2004; 52(2‐3):200  263. · 0.98 Impact Factor
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