26,818 research outputs found
Does The Force From an Extra Dimension Contradict Physics in 4D?
We examine the question of whether violation of 4D physics is an inevitable
consequence of existence of an extra non-compactified dimension. Recent
investigations in membrane and Kaluza-Klein theory indicate that when the
metric of the spacetime is allowed to depend on the extra coordinate, i.e., the
cilindricity condition is dropped, the equation describing the trajectory of a
particle in one lower dimension has an extra force with some abnormal
properties. Among them, a force term parallel to the four-velocity of the
particle and, what is perhaps more surprising,
. These properties violate basic concepts
in 4D physics. In this paper we argue that these abnormal properties are {\em
not} consequence of the extra dimension, but result from the formalism used. We
propose a new definition for the force, from the extra dimension, which is free
of any contradictions and consistent with usual 4D physics. We show, using
warp-products metrics, that this new definition is also more consistent with
our physical intuition. The effects of this force could be detected observing
objects moving with high speed, near black holes and/or in cosmological
situations.Comment: Minor addition in the Introduction to match the version to appear in
Phys. Lett.
Brane-world models emerging from collisions of plane waves in 5D
We consider brane-world models embedded in a five-dimensional bulk spacetime
with a large extra dimension and a cosmological constant. The cosmology in
possesses "wave-like" character in the sense that the metric coefficients in
the bulk are assumed to have the form of plane waves propagating in the fifth
dimension. We model the brane as the "plane" of collision of waves propagating
in opposite directions along the extra dimension. This plane is a jump
discontinuity which presents the usual symmetry of brane models.
The model reproduces the {\em generalized} Friedmann equation for the evolution
on the brane, regardless of the specific details in . Model solutions with
spacelike extra coordinate show the usual {\em big-bang} behavior, while those
with timelike extra dimension present a {\em big bounce}. This bounce is an
genuine effect of a timelike extra dimension. We argue that, based on our
current knowledge, models having a large timelike extra dimension cannot be
dismissed as mathematical curiosities in non-physical solutions. The size of
the extra dimension is small today, but it is {\em increasing} if the universe
is expanding with acceleration. Also, the expansion rate of the fifth dimension
can be expressed in a simple way through the four-dimensional "deceleration"
and Hubble parameters as . These predictions could have important
observational implications, notably for the time variation of rest mass,
electric charge and the gravitational "constant". They hold for the three models with arbitrary cosmological constant, and are independent
of the signature of the extra dimension.Comment: In V2 the signature of the extra dimension is discussed and new
references are added. In V3 typos are correcte
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