648 research outputs found
Fundamental constants and tests of general relativity - Theoretical and cosmological considerations
The tests of the constancy of the fundamental constants are tests of the
local position invariance and thus of the equivalence principle. We summarize
the various constraints that have been obtained and then describe the
connection between varying constants and extensions of general relativity. To
finish, we discuss the link with cosmology, and more particularly with the
acceleration of the Universe. We take the opportunity to summarize various
possibilities to test general relativity (but also the Copernican principle) on
cosmological scales.Comment: Proceedings of the workshop ``The nature of gravity, confronting
theory and experiment in space'', ISSI, Bern, october 200
Brane-World Motion in Compact Dimensions
The topology of extra dimensions can break global Lorentz invariance,singling
out a globally preferred frame even in flat spacetime. Through experiments that
probe global topology, an observer can determine her state of motion with
respect to the preferred frame. This scenario is realized if we live on a brane
universe moving through a flat space with compact extra dimensions. We identify
three experimental effects due to the motion of our universe that one could
potentially detect using gravitational probes. One of these relates to the
peculiar properties of the twin paradox in multiply-connected spacetimes.
Another relies on the fact that the Kaluza-Klein modes of any bulk field are
sensitive to boundary conditions. A third concerns the modification to the
Newtonian potential on a moving brane. Remarkably, we find that even small
extra dimensions are detectable by brane observers if the brane is moving
sufficiently fast
`c' is the speed of light, isn't it?
Theories proposing a varying speed of light have recently been widely
promoted under the claim that they offer an alternative way of solving the
standard cosmological problems. Recent observational hints that the fine
structure constant may have varied during over cosmological scales also has
given impetus to these models. In theoretical physics the speed of light, ,
is hidden in almost all equations but with different facets that we try to
distinguish. Together with a reminder on scalar-tensor theories of gravity,
this sheds some light on these proposed varying speed of light theories.Comment: 14 pages, Late
Probing dark energy beyond with CODEX
Precision measurements of nature's fundamental couplings and a first
measurement of the cosmological redshift drift are two of the key targets for
future high-resolution ultra-stable spectrographs such as CODEX. Being able to
do both gives CODEX a unique advantage, allowing it to probe dynamical dark
energy models (by measuring the behavior of their equation of state) deep in
the matter era and thereby testing classes of models that would otherwise be
difficult to distinguish from the standard CDM paradigm. We illustrate
this point with two simple case studies.Comment: 4 pages, 4 figures; submitted to Phys. Rev.
Distinguishing Marks of Simply-connected Universes
A statistical quantity suitable for distinguishing simply-connected
Robertson-Walker (RW) universes is introduced, and its explicit expressions for
the three possible classes of simply-connected RW universes with an uniform
distribution of matter are determined. Graphs of the distinguishing mark for
each class of RW universes are presented and analyzed.There sprout from our
results an improvement on the procedure to extract the topological signature of
multiply-connected RW universes, and a refined understanding of that
topological signature of these universes studied in previous works.Comment: 13 pages, 4 figures, LaTeX2e. To appear in Int. J. Mod. Phys. D
(2000
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