367 research outputs found
Stability of Scalar Fields in Warped Extra Dimensions
This work sets up a general theoretical framework to study stability of
models with a warped extra dimension where N scalar fields couple minimally to
gravity. Our analysis encompasses Randall-Sundrum models with branes and bulk
scalars, and general domain-wall models. We derive the Schrodinger equation
governing the spin-0 spectrum of perturbations of such a system. This result is
specialized to potentials generated using fake supergravity, and we show that
models without branes are free of tachyonic modes. Turning to the existence of
zero modes, we prove a criterion which relates the number of normalizable zero
modes to the parities of the scalar fields. Constructions with definite parity
and only odd scalars are shown to be free of zero modes and are hence
perturbatively stable. We give two explicit examples of domain-wall models with
a soft wall, one which admits a zero mode and one which does not. The latter is
an example of a model that stabilizes a compact extra dimension using only bulk
scalars and does not require dynamical branes.Comment: 25 pages, 2 figures; v2: minor changes to text, references added,
matches published versio
Signatures of Large Extra Dimensions
String theory suggests modifications of our spacetime such as extra
dimensions and the existence of a mininal length scale. In models with
addidional dimensions, the Planck scale can be lowered to values accessible by
future colliders. Effective theories which extend beyond the standart-model by
including extra dimensions and a minimal length allow computation of
observables and can be used to make testable predictions. Expected effects that
arise within these models are the production of gravitons and black holes.
Furthermore, the Planck-length is a lower bound to the possible resolution of
spacetime which might be reached soon.Comment: 8 pages, no figures, Talk presented at the NATO Advanced Study
Institute: Structure and Dynamics of Elementary Matter, Kemer, Turkey, 22 Sep
- 2 Oct 2003. Proceedings to be published by Kluwer Academic publisher
The influence of D-branes' backreaction upon gravitational interactions between open strings
We argue that gravitational interactions between open strings ending on
D3-branes are largely shaped by the D3-branes' backreaction. To this end we
consider classical open strings coupled to general relativity in Poincare AdS5
backgrounds. We compute the linear gravitational backreaction of a static
string extending up to the Poincare horizon, and deduce the potential energy
between two such strings. If spacetime is non-compact, we find that the
gravitational potential energy between parallel open strings is independent of
the strings' inertial masses and goes like 1/r at large distance r. If the
space transverse to the D3-branes is suitably compactified, a collective mode
of the graviton propagates usual four-dimensional gravity. In that case the
backreaction of the D3-branes induces a correction to the Newtonian potential
energy that violates the equivalence principle. The observed enhancement of the
gravitational attraction is specific to string theory; there is no similar
effect for point-particles.Comment: 28 pages, 7 figures. Typos corrected, minor addition
Spacetime Noncommutativity in Models with Warped Extradimensions
We construct consistent noncommutative (NC) deformations of the
Randall-Sundrum spacetime that solve the NC Einstein equations with a
non-trivial Poisson tensor depending on the fifth coordinate. In a class of
these deformations where the Poisson tensor is exponentially localized on one
of the branes (the NC-brane), we study the effects on bulk particles in terms
of Lorentz-violating operators induced by NC-brane interactions. We sketch two
models in which massive bulk particles mediate NC effects to an
almost-commutative SM-brane, such that observables at high energy colliders are
enhanced with respect to low energy and astrophysical observables.Comment: 15 pages, LaTeX, pdf figures included, to appear in JHE
Enhanced Eyelashes: Prescription and Over-the-Counter Options
Women have long strived to possess long, thick, and dark eyelashes. Prominent eyes and eyelashes are often considered a sign of beauty and can be associated with increased levels of attractiveness, confidence, and well-being. Numerous options may improve the appearance of eyelashes. Mascara aims to temporarily darken, lengthen, and thicken eyelashes using a combination of waxes, pigments, and resins. Artificial eyelashes can be adhered either to the dermal margin or to individual eyelashes. Individuals may even use eyelash transplantations to improve the appearance of their eyelashes. The unique properties of eyelashes (e.g., relatively long telogen and short anagen phases compared with scalp hairs, slow rate of growth, and a lack of influence by androgens) may allow for specific aesthetic interventions to improve the appearance of natural eyelashes. Some over-the-counter (OTC) products may contain prostaglandin analogs that can affect eyelash growth, but neither the safety nor efficacy of these OTC cosmetics has been fully studied. Originally indicated for the reduction of intraocular pressure, the synthetic prostaglandin analog bimatoprost was recently approved for the treatment of hypotrichosis of the eyelashes. In a double-blinded, randomized, vehicle-controlled trial, bimatoprost safely and effectively grew natural eyelashes, making them longer, thicker, and darker. Bimatoprost was generally safe and well tolerated and appears to provide an additional option for individuals looking to improve the appearance of their eyelashes
Lorentz Violation in Warped Extra Dimensions
Higher dimensional theories which address some of the problematic issues of
the Standard Model(SM) naturally involve some form of -dimensional
Lorentz invariance violation (LIV). In such models the fundamental physics
which leads to, e.g., field localization, orbifolding, the existence of brane
terms and the compactification process all can introduce LIV in the higher
dimensional theory while still preserving 4-d Lorentz invariance. In this
paper, attempting to capture some of this physics, we extend our previous
analysis of LIV in 5-d UED-type models to those with 5-d warped extra
dimensions. To be specific, we employ the 5-d analog of the SM Extension of
Kostelecky et. al. ~which incorporates a complete set of operators arising from
spontaneous LIV. We show that while the response of the bulk scalar, fermion
and gauge fields to the addition of LIV operators in warped models is
qualitatively similar to what happens in the flat 5-d UED case, the gravity
sector of these models reacts very differently than in flat space.
Specifically, we show that LIV in this warped case leads to a non-zero bulk
mass for the 5-d graviton and so the would-be zero mode, which we identify as
the usual 4-d graviton, must necessarily become massive. The origin of this
mass term is the simultaneous existence of the constant non-zero
curvature and the loss of general co-ordinate invariance via LIV in the 5-d
theory. Thus warped 5-d models with LIV in the gravity sector are not
phenomenologically viable.Comment: 14 pages, 4 figs; discussion added, algebra repaire
Spin-2 spectrum of defect theories
We study spin-2 excitations in the background of the recently-discovered
type-IIB solutions of D'Hoker et al. These are holographically-dual to defect
conformal field theories, and they are also of interest in the context of the
Karch-Randall proposal for a string-theory embedding of localized gravity. We
first generalize an argument by Csaki et al to show that for any solution with
four-dimensional anti-de Sitter, Poincare or de Sitter invariance the spin-2
excitations obey the massless scalar wave equation in ten dimensions. For the
interface solutions at hand this reduces to a Laplace-Beltrami equation on a
Riemann surface with disk topology, and in the simplest case of the
supersymmetric Janus solution it further reduces to an ordinary differential
equation known as Heun's equation. We solve this equation numerically, and
exhibit the spectrum as a function of the dilaton-jump parameter .
In the limit of large a nearly-flat linear-dilaton dimension grows
large, and the Janus geometry becomes effectively five-dimensional. We also
discuss the difficulties of localizing four-dimensional gravity in the more
general backgrounds with NS5-brane or D5-brane charge, which will be analyzed
in detail in a companion paper.Comment: 41 pages, 6 figure
Constraints on Non-Newtonian Gravity from Recent Casimir Force Measurements
Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.Comment: 20 pages, crckbked.cls is used, to be published in: Proceedings of
the 18th Course of the School on Cosmology and Gravitation: The Gravitational
Constant. Generalized Gravitational Theories and Experiments (30 April- 10
May 2003, Erice). Ed. by G. T. Gillies, V. N. Melnikov and V. de Sabbata,
20pp. (Kluwer, in print, 2003
de Sitter Thick Brane Solution in Weyl Geometry
In this paper, we consider a de Sitter thick brane model in a pure geometric
Weyl integrable five-dimensional space-time, which is a generalization of
Riemann geometry and is invariant under a so-called Weyl rescaling. We find a
solution of this model via performing a conformal transformation to map the
Weylian structure into a familiar Riemannian one with a conformal metric. The
metric perturbations of the model are discussed. For gravitational
perturbation, we get the effective modified Pschl-Teller
potential in corresponding Schrdinger equation for
Kaluza-Klein (KK) modes of the graviton. There is only one bound state, which
is a normalizable massless zero mode and represents a stable 4-dimensional
graviton. Furthermore, there exists a mass gap between the massless mode and
continuous KK modes. We also find that the model is stable under the scalar
perturbation in the metric. The correction to the Newtonian potential on the
brane is proportional to , where is the de Sitter
parameter of the brane. This is very different from the correction caused by a
volcano-like effective potential.Comment: 24 pages, 13 figures, published versio
- âŠ