3,109 research outputs found

### Defect Formation with Bulk Fields

It has recently been realized that brane-antibrane annihilation (a possible
explanation for ending inflation) may result in defect formation, due to the
dynamics of the tachyon field. Studies of this possibility have generally
ignored the interaction of the brane fields with fields in the bulk; recently
it has been argued [1] that interactions with bulk fields suppress or even
eliminate defect formation.
To investigate the impact of bulk fields on brane defect formation, we
construct a toy model that captures the essential features of the tachyon
condensation with bulk fields. We study the structure of defects in this toy
model, and simulate their formation and evolution on the lattice. We find that,
while the energetics and interactions of defects are influenced by the size of
the extra dimension and the bulk-brane coupling, the bulk-brane coupling does
not prevent the formation of a defect network.Comment: 23 pages, 5 figures, revtex4, 2 appendices adde

### Origin of matter out of pure curvature

We propose a mechanism for origin of matter in the universe in the framework
of Einstein-Gauss-Bonnet gravity in higher dimensions. The recently discovered
new static black hole solution by the authors \cite{md2006} with the
Kaluza-Klein split up of spacetime as a product of the usual {\ma M}^4 with a
space of negative constant curvature is indeed a pure gravitational creation of
a black hole which is also endowed with a Maxwell-like {\it gravitational
charge} in four-dimensional vacuum spacetime. Further it could be envisioned as
being formed from anti-de Sitter spacetime by collapse of radially inflowing
charged null dust. It thus establishes the remarkable reciprocity between
matter and gravity - as matter produces gravity (curvature), gravity too
produces matter.Comment: 8 pages, 1 Fig, Received Honorable Mention in 2007 GRF Essay
Competition, Summary of the talk given at Himalayan Relativity Dialogue at
Mirik, April 18-20, 200

### Kaluza-Klein black hole with negatively curved extra dimensions in string generated gravity models

We obtain a new exact black-hole solution in Einstein-Gauss-Bonnet gravity
with a cosmological constant which bears a specific relation to the
Gauss-Bonnet coupling constant. The spacetime is a product of the usual
4-dimensional manifold with a $(n-4)$-dimensional space of constant negative
curvature, i.e., its topology is locally {\ma M}^n \approx {\ma M}^4 \times
{\ma H}^{n-4}. The solution has two parameters and asymptotically approximates
to the field of a charged black hole in anti-de Sitter spacetime. The most
interesting and remarkable feature is that the Gauss-Bonnet term acts like a
Maxwell source for large $r$ while at the other end it regularizes the metric
and weakens the central singularity.Comment: 4 pages, 2 figures, final version to appear in Physical Review D as a
rapid communicatio

### The dynamical Casimir effect in braneworlds

In braneworld cosmology the expanding Universe is realized as a brane moving
through a warped higher-dimensional spacetime. Like a moving mirror causes the
creation of photons out of vacuum fluctuations, a moving brane leads to
graviton production. We show that, very generically, Kaluza-Klein (KK)
particles scale like stiff matter with the expansion of the Universe and can
therefore not represent the dark matter in a warped braneworld. We present
results for the production of massless and KK gravitons for bouncing branes in
five-dimensional anti de Sitter space. We find that for a realistic bounce the
back reaction from the generated gravitons will be most likely relevant. This
letter summarizes the main results and conclusions from numerical simulations
which are presented in detail in a long paper [M.Ruser and R. Durrer, Phys.
Rev. D 76, 104014 (2007), arXiv:0704.0790]Comment: misprints corrected, matches published versio

### New Hints from General Relativity

The search for a quantum theory of gravity has followed two parallel but
different paths. One aims at arriving at the final theory starting from a
priori assumptions as to its form and building it from the ground up. The other
tries to infer as much as possible about the unknown theory from the existing
ones and use our current knowledge to constrain the possibilities for the
quantum theory of gravity. Probably the biggest success of the second path has
been the results of black hole thermodynamics. The subject of this essay is a
new, highly promising such result, the application of quasinormal modes in
quantum gravity.Comment: This essay received an "honorable mention" in the 2003 Essay
Competition of the Gravity Research Foundatio

### D3-branes dynamics and black holes

Using the D3-brane as the fundamental tool, we adress two aspects of D-branes
physics. The first regards the interaction between two electromagnetic dual
D-branes in 10 dimensions. In particular, we give a meaning to {\it both} even
and odd spin structure contributions, the latter being non vanishing for non
zero relative velocity $v$ (and encoding the Lorentz-like contribution). The
second aspect regards the D-brane/black holes correspondence. We show how the 4
dimensional configuration corresponding to a {\it single} D3-brane wrapped on
the orbifold T^6/Z_3 represents a regular Reissner-Nordstrom solution of d=4
N=2 supergravityComment: 8 pages, latex, 1 eps figure. Talk presented by M. Bertolini at the
conference "Quantum aspects of gauge theories, supergravity and unification"
in Corfu`; to appear in the proceeding

### Path integral evaluation of Dbrane amplitudes

We extend Polchinski's evaluation of the measure for the one-loop closed
string path integral to open string tree amplitudes with boundaries and
crosscaps embedded in Dbranes. We explain how the nonabelian limit of
near-coincident Dbranes emerges in the path integral formalism. We give a
careful path integral derivation of the cylinder amplitude including the
modulus dependence of the volume of the conformal Killing group.Comment: Extended version replacing hep-th/9903184, includes discussion of
nonabelian limit, Latex, 10 page

### Moduli Stabilization with the String Higgs Effect

We review the notion of the Higgs effect in the context of string theory. We
find that by including this effect in time dependent backgrounds, one is led to
a natural mechanism for stabilizing moduli at points of enhanced gauge
symmetry. We consider this mechanism for the case of the radion (size of the
extra dimensions) and find that as decompactification of the large spatial
dimensions takes place the radion will remain stabilized at the self dual
radius. We discuss how this mechanism can be incorporated into models of string
cosmology and brane inflation to resolve some outstanding problems. We also
address some issues regarding which string states should be included when
constructing low energy actions in string cosmology.Comment: 20 pages, references added, typos correcte

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