32 research outputs found
Cosmological constant and gravitational theory on D-brane
In a toy model we derive the gravitational equation on a self-gravitating
curved D-brane. The effective theory on the brane is drastically changed from
the ordinal Einstein equation. The net cosmological constant on the brane
depends on a tuning between the brane tension and the brane charges. Moreover,
non-zero matter stress tensor exists if the net cosmological constant is not
zero. This fact indicates a direct connection between matters on the brane and
the dark energy.Comment: 6 pages, minor corrections, accepted for publication in Physical
Review
Can we live on a D-brane? -- Effective theory on a self-gravitating D-brane --
We consider a D-brane coupled with gravity in type IIB supergravity on S^5
and derive the effective theory on the D-brane in two different ways, that is,
holographic and geometrical projection methods. We find that the effective
equations on the brane obtained by these methods coincide. The theory on the
D-brane described by the Born-Infeld action is not like Einstein-Maxwell theory
in the lower order of the gradient expansion, i.e., the Maxwell field does not
appear in the theory. Thus the careful analysis and statement for cosmology on
self-gravitating D-brane should be demanded in realistic models.Comment: 13 pages, accepted for publication in Physical Review
D-braneworld cosmology
We discuss D-braneworld cosmology, that is, the brane is described by the
Born-Infeld action. Compared with the usual Randall-Sundrum braneworld
cosmology where the brane action is the Nambu-Goto one, we can see some drastic
changes at the very early universe: (i)universe may experience the rapid
accelerating phase (ii)the closed universe may avoid the initial singularity.
We also briefly address the dynamics of the cosmology in the open string
metric, which might be favorer than the induced metric from the view point of
the D-brane.Comment: 6 pages, 3 figures, minor corrections, accepted for publication in
Phys. Rev.
Brane-World and Holography
We consider the brane-world in the holographic point of view. Bearing the
realistic models in mind, the bulk massless scalar field is introduced. First
of all, we find the constraint on the coupling of the scalar fields with the
matter(not holographic CFT) on the brane. We show that the traceless part of
the energy-momentum tensor of holographic CFT is a part of the bulk Weyl
tensor. The trace part which comes from the trace-anomaly is corresponding to
the -term appeared in the generalized FRW equation in the brane-world.Comment: 4 pages, minor change
Do naked singularities generically occur in generalized theories of gravity?
A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.Comment: 4 pages including 2 eps figures, to be published in Physical Review
Letter
The keratin-binding protein Albatross regulates polarization of epithelial cells
The keratin intermediate filament network is abundant in epithelial cells, but its function in the establishment and maintenance of cell polarity is unclear. Here, we show that Albatross complexes with Par3 to regulate formation of the apical junctional complex (AJC) and maintain lateral membrane identity. In nonpolarized epithelial cells, Albatross localizes with keratin filaments, whereas in polarized epithelial cells, Albatross is primarily localized in the vicinity of the AJC. Knockdown of Albatross in polarized cells causes a disappearance of key components of the AJC at cellâcell borders and keratin filament reorganization. Lateral proteins E-cadherin and desmoglein 2 were mislocalized even on the apical side. Although Albatross promotes localization of Par3 to the AJC, Par3 and ezrin are still retained at the apical surface in Albatross knockdown cells, which retain intact microvilli. Analysis of keratin-deficient epithelial cells revealed that keratins are required to stabilize the Albatross protein, thus promoting the formation of AJC. We propose that keratins and the keratin-binding protein Albatross are important for epithelial cell polarization
Radionic Non-uniform Black Strings
Non-uniform black strings in the two-brane system are investigated using the
effective action approach. It is shown that the radion acts as a non-trivial
hair of the black strings. From the brane point of view, the black string
appears as the deformed dilatonic black hole which becomes dilatonic black hole
in the single brane limit and reduces to the Reissner-Nordstr\"om black hole in
the close limit of two-branes. The stability of solutions is demonstrated using
the catastrophe theory. From the bulk point of view, the black strings are
proved to be non-uniform. Nevertheless, the zeroth law of black hole
thermodynamics still holds.Comment: 9 pages, 6 figure
Effective Gravitational Equations on Brane World with Induced Gravity
We present the effective equations to describe the four-dimensional gravity
of a brane world, assuming that a five-dimensional bulk spacetime satisfies the
Einstein equations and gravity is confined on the symmetric brane.
Applying this formalism, we study the induced-gravity brane model first
proposed by Dvali, Gabadadze and Porrati. In a generalization of their model,
we show that an effective cosmological constant on the brane can be extremely
reduced in contrast to the case of the Randall-Sundrum model even if a bulk
cosmological constant and a brane tension are not fine-tuned.Comment: 8 pages, 1 figure, final version to appear in Physical Review
Small localized black holes in a braneworld: Formulation and numerical method
No realistic black holes localized on a 3-brane in the Randall-Sundrum
infinite braneworld have been found so far. The problem of finding a static
black hole solution is reduced to a boundary value problem. We solve it by
means of a numerical method, and show numerical examples of a localized black
hole whose horizon radius is small compared to the bulk curvature scale. The
sequence of small localized black holes exhibits a smooth transition from a
five-dimensional Schwarzschild black hole, which is a solution in the limit of
small horizon radius. The localized black hole tends to flatten as its horizon
radius increases. However, it becomes difficult to find black hole solutions as
its horizon radius increases.Comment: RevTeX, 13 pages, 6 figures, references corrected, typos corrected;
to appear in Phys.Rev.