28 research outputs found
Homotopy Structure of 5d Vacua
It is shown that flat zero-energy solutions (vacua) of the 5d Kaluza-Klein
theory admit a non-trivial homotopy structure generated by certain Kaluza-Klein
excitations. These vacua consist of an infinite set of homotopically different
spacetimes denoted by , among which
and are especially identified as and
, the ground states of the 5d Kaluza-Klein theory and the 5d general
relativity, respectively (where represents the -dimensional Minkowski
space).Comment: 8 page
Time Evolution as a Gauge Transformation: x^5-dependent Cosmological Solution in 5d Kaluza-Klein Theory
We discuss a new feature of the 5d Kaluza-Klein cosmology. For that purpose,
we obtain the simplest x^5-dependent solution which, in the reduced
description, is associated with a radiation-dominated Robertson-Walker
universe, and also can be regarded as an extension of the Schwarzschild
solution. This solution enables us to deduce an important result that an
evolving universe is related with a static universe by the gauge
transformation, i.e., they are gauge equivalent. This means that having a
different universe simply corresponds to choosing a different gaugeComment: latex, 14page
A self-tuning mechanism in (3+p)d gravity-scalar theory
We present a new type of self-tuning mechanism for ()d brane world
models in the framework of gravity-scalar theory. This new type of self-tuning
mechanism exhibits a remarkable feature. In the limit , being
the string coupling, the geometry of bulk spacetime remains virtually unchanged
by an introduction of the Standard Model(SM)-brane, and consequently it is
virtually unaffected by quantum fluctuations of SM fields with support on the
SM-brane. Such a feature can be obtained by introducing Neveu-Schwarz(NS)-brane
as a background brane on which our SM-brane is to be set. Indeed, field
equations naturally suggest the existence of the background NS-brane. Among the
given such models, of the most interest is the case with , where
represents the bulk cosmological constant. This model contains a pair
of coincident branes (of the SM- and the NS-branes), one of which is a
codimension-2 brane placed at the origin of 2d transverse space (), another a codimension-1 brane placed at the edge of .
These two branes are (anti) T-duals of each other, and one of them may be
identified as our SM-brane plus the background NS-brane. In the presence of the
background NS-brane (and in the absence of ), the 2d transverse space
becomes an orbifold with an appropriate deficit angle.
But this is only possible if the ()d Planck scale and the string
scale () are of the same order, which
accords with the hierarchy assumption \cite{1,2,3} that the electroweak scale
is the only short distance scale existing in nature
A comment on -branes of () string theory
We argue that in ()d string theory the existence of NS-NS type -brane
with negative tension is essential to obtain background geometry or on the transverse dimensions, and the usual codimension-2 brane
solutions with these background geometries already contain the negative tension
NS-brane implicity in their ansatz. Such an argument leads us, in the context
of brane world scenarios, to a conjecture that true background -brane
immanent in our spacetime may perhaps be NS-NS type brane, rather than D-brane.Comment: 16 pages. Version to appear in JHE
D-brane orbiting NS5-branes
We study real time dynamics of a Dp-brane orbiting a stack of NS5-branes. It
is generally known that a BPS D-brane moving in the vicinity of NS5-branes
becomes unstable due to the presence of tachyonic degree of freedom induced on
the D-brane. Indeed, the D-brane necessarily falls into the fivebranes due to
gravitational attraction and eventually collapses into a pressureless fluid.
Such a decay of the D-brane is known to be closely related to the rolling
tachyon problem. In this paper we show that in special cases the decay of
D-brane caused by gravitational attraction can be avoided. Namely for certain
values of energy and angular momentum the D-brane orbits around the fivebranes,
maintaining certain distance from the fivebranes all the time, and the process
of tachyon condensation is suppressed. We show that the tachyonic degree of
freedom induced on such a D-brane really disappears and the brane returns to a
stable D-brane.Comment: 12 pages, latex, added referenc