569 research outputs found
A Small Cosmological Constant and Backreaction of Non-Finetuned Parameters
We include the backreaction on the warped geometry induced by non-finetuned
parameters in a two domain-wall set-up to obtain an exponentially small
Cosmological Constant . The mechanism to suppress the Cosmological
Constant involves one classical fine-tuning as compared to an infinity of
finetunings at the quantum level in standard D=4 field theory.Comment: 13 pages, minor corrections and references adde
Modulus Stabilization with Bulk Fields
We propose a mechanism for stabilizing the size of the extra dimension in the
Randall-Sundrum scenario. The potential for the modulus field that sets the
size of the fifth dimension is generated by a bulk scalar with quartic
interactions localized on the two 3-branes. The minimum of this potential
yields a compactification scale that solves the hierarchy problem without fine
tuning of parameters.Comment: 8 pages, LaTeX; minor typo correcte
Topological Insulators and Superconductors from String Theory
Topological insulators and superconductors in different spatial dimensions
and with different discrete symmetries have been fully classified recently,
revealing a periodic structure for the pattern of possible types of topological
insulators and supercondutors, both in terms of spatial dimensions and in terms
of symmetry classes. It was proposed that K-theory is behind the periodicity.
On the other hand, D-branes, a solitonic object in string theory, are also
known to be classified by K-theory. In this paper, by inspecting low-energy
effective field theories realized by two parallel D-branes, we establish a
one-to-one correspondence between the K-theory classification of topological
insulators/superconductors and D-brane charges. In addition, the string theory
realization of topological insulators and superconductors comes naturally with
gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a
gauge field theory of topological nature, such as ones with the Chern-Simons
term or the -term in various dimensions. This sheds light on
topological insulators and superconductors beyond non-interacting systems, and
the underlying topological field theory description thereof. In particular, our
string theory realization includes the honeycomb lattice Kitaev model in two
spatial dimensions, and its higher-dimensional extensions. Increasing the
number of D-branes naturally leads to a realization of topological insulators
and superconductors in terms of holography (AdS/CFT).Comment: 13 pages, 3 figures;references update
Cosmology in a brane-universe
This contribution presents the cosmological models with extra dimensions that
have been recently elaborated, which assume that ordinary matter is confined on
a surface, called brane, embedded in a higher dimensional spacetime.Comment: 12 pages; Invited review talk at the JENAM 2002 workshop on "The
cosmology of extra dimensions and varying fundamental constants", Porto,
Portugal, September 200
Orientifold and Type II Dual Pairs
In this paper we present a symmetry of a toroidally compactified type II
string theory. This symmetry has the interpretaion that it interchanges the
left and the right-moving worldsheet coordinates and reverses the orientations
of some of the spatial coordinates. We also identify another discrete symmetry
of the type II theory which is related to the above one by a nontrivial
U-duality element of string theory. This symmetry, however, has trivial action
on the worldsheet coordinates and corresponds to an improper T-duality
rotation. We then construct examples of type II dual pairs in four dimensions
by modding out the known type II dual pairs by the above symmetries. We show
the explicit matching of the spectrum and supersymmetries in these examples.Comment: 17 page
Gravitational Couplings and Orientifolds
The interplay between gravitational couplings on branes and the occurrence of
fractional flux in low dimensional orientifolds is examined. It is argued that
gravitational couplings need to be assigned not only to D-branes but also to
orientifold planes. The fractional charges of the orientifold -planes can be
understood in terms of flux quantization of the form potential and
modified Bianchi identities. Detailed results are presented for the case of the
type IIB orientifold on , which is dual to F-theory on a complex
4-fold with terminal singularities.Comment: 24 pages, harvmac,Numerical coefficients of R^4 couplings have been
corrected, and are now in agreement with recent results of hep-th/9812071 and
hep-th/9812088. No other changes. This revision supercedes the published
version of this pape
M-theory Inspired No-scale Supergravity
We propose a supergravity model that contains elements recently shown to
arise in the strongly-coupled limit of the heterotic string
(M-theory), including a no-scale--like K\"ahler potential, the identification
of the string scale with the gauge coupling unification scale, and the onset of
supersymmetry breaking at an intermediate scale determined by the size of the
eleventh dimension of M-theory. We also study the phenomenological consequences
of such scenario, which include a rather constrained sparticle spectrum within
the reach of present-generation particle accelerators.Comment: 8 pages, LaTeX, 3 figures (included
Exact gravitational lensing and rotation curve
Based on the geodesic equation in a static spherically symmetric metric we
discuss the rotation curve and gravitational lensing. The rotation curve
determines one function in the metric without assuming Einstein's equations.
Then lensing is considered in the weak field approximation of general
relativity. From the null geodesics we derive the lensing equation and
corrections to it.Comment: 12 pages, 1 figur
Fate of Kaluza-Klein Bubble
We numerically study classical time evolutions of Kaluza-Klein bubble
space-time which has negative energy after a decay of vacuum. As the zero
energy Witten's bubble space-time, where the bubble expands infinitely, the
subsequent evolutions of Brill and Horowitz's momentarily static initial data
show that the bubble will expand in terms of the area. At first glance, this
result may support Corley and Jacobson's conjecture that the bubble will expand
forever as well as the Witten's bubble. The irregular signatures, however, can
be seen in the behavior of the lapse function in the maximal slicing gauge and
the divergence of the Kretchman invariant. Since there is no appearance of the
apparent horizon, we suspect an appearance of a naked singularity as the final
fate of this space-time.Comment: 13 pages including 10 figures, RevTeX, epsf.sty. CGPG-99/12-8,
RESCEU-6/00 and DAMTP-2000-30. To appear in Phys. Rev.
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