363 research outputs found
Supersymmetry Breaking and Inflation from Higher Curvature Supergravity
The generic embedding of the higher curvature theory into old-minimal
supergravity leads to models with rich vacuum structure in addition to its
well-known inflationary properties. When the model enjoys an exact R-symmetry,
there is an inflationary phase with a single supersymmetric Minkowski vacuum.
This appears to be a special case of a more generic set-up, which in principle
may include R-symmetry violating terms which are still of pure supergravity
origin. By including the latter terms, we find new supersymmetry breaking vacua
compatible with single-field inflationary trajectories. We discuss explicitly
two such models and we illustrate how the inflaton is driven towards the
supersymmetry breaking vacuum after the inflationary phase. In these models the
gravitino mass is of the same order as the inflaton mass. Therefore, pure
higher curvature supergravity may not only accommodate the proper inflaton
field, but it may also provide the appropriate hidden sector for supersymmetry
breaking after inflation has ended.Comment: 41 pages, 21 figures, published versio
Octonionic Gravitational Instantons
We construct eight-dimensional gravitational instantons by solving
appropriate self-duality equations for the spin-connection. The particular
gravitational instanton we present has holonomy and, in a sense, it
is the eight-dimensional analog of the Eguchi-Hanson 4D space. It has a
removable bolt singularity which is topologically S^4 and its boundary at
infinity is the squashed S^7. We also lift our solutions to ten and eleven
dimensions and construct fundamental string and membrane configurations that
preserve 1/16 of the original supersymmetries.Comment: 17 pages, latex, no figures. References to earlier works adde
4d-Flat Compactifications With Brane Vorticities
We present solutions in six-dimensional gravity coupled to a sigma model, in
the presence of three-brane sources. The space transverse to the branes is a
compact non-singular manifold. The example of O(3) sigma model in the presence
of two three-branes is worked out in detail. We show that the four-dimensional
flatness is obtained with a single condition involving the brane tensions,
which are in general different and may be both positive, and another
characteristic of the branes, vorticity. We speculate that the adjustment of
the effective four-dimensional cosmological constant may occur through the
exchange of vorticity between the branes. We then give exact instanton type
solutions for sigma models targeted on a general K\"ahler manifold, and
elaborate in this framework on multi-instantons of the O(3) sigma model. The
latter have branes, possibly with vorticities, at the instanton positions, thus
generalizing our two-brane solution.Comment: 8 pages. New references added and minor typos are correcte
Beta-functions in Yang-Mills Theory from Non-critical String
The renormalization group equations of the Yang-Mills theory are examined in
the non-critical string theory according to the framework of the holography.
Under a simple ansatz for the tachyon, we could find several interesting
solutions which are classified by the value of the tachyon potential at the
vacuum. We show two typical, asymptotic-free solutions which are different in
their infrared behaviors. For both types of solutions, we could obtain
quark-confinement potential from the Wilson-loop. The stability of the tachyon
and the ZigZag symmetry are also discussed for these solutions.Comment: 16 pages, 5 figure
Yang-Mills theory from non-critical string
The correspondence of the non-critical string theory and the Yang-Mills
theory is examined according to the recent Polyakov's proposal, and two
possible solutions of the bulk equations are addressed near the fixed points of
the pure Yang-Mills theory: (i) One solution asymptotically approaches to the
AdS space at the ultraviolet limit where the conformally invariant field theory
is realized. (ii) The second one approaches to the flat space in both the
infrared and the ultraviolet limits. The area law of the Wilson-loop and the
asymptotic freedom with logarithmic behaviour are seen in the respective limit.Comment: 17 pages, no figure, Late
Braneworld inflation
We discuss various realizations of the four dimensional braneworld inflation
in warped geometries of string theory. In all models the inflaton field is
represented by a Dp probe brane scalar specifying its position in the warped
throat of the compactification manifold. We study existing inflationary throat
local geometries, and construct a new example. The inflationary brane is either
a D3- or a D5-brane of type IIB string theory. In the latter case the
inflationary brane is wrapping a two-cycle of the compactification manifold. We
discuss some phenomenological aspects of the model where slow-roll conditions
are under computational control.Comment: 31 pages + 6 figures, v2: published PRD versio
Cosmic Acceleration Driven by Mirage Inhomogeneities
A cosmological model based on an inhomogeneous D3-brane moving in an AdS_5 X
S_5 bulk is introduced. Although there is no special points in the bulk, the
brane Universe has a center and is isotropic around it. The model has an
accelerating expansion and its effective cosmological constant is inversely
proportional to the distance from the center, giving a possible geometrical
origin for the smallness of a present-day cosmological constant. Besides, if
our model is considered as an alternative of early time acceleration, it is
shown that the early stage accelerating phase ends in a dust dominated FRW
homogeneous Universe. Mirage-driven acceleration thus provides a dark matter
component for the brane Universe final state. We finally show that the model
fulfills the current constraints on inhomogeneities.Comment: 14 pages, 1 figure, IOP style. v2, changed style, minor corrections,
references added, version accepted in Class. Quant. Gra
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
Gauge-invariant fluctuations of scalar branes
A generalization of the Bardeen formalism to the case of warped geometries is
presented. The system determining the gauge-invariant fluctuations of the
metric induced by the scalar fluctuations of the brane is reduced to a set of
Schr\"odinger-like equations for the Bardeen potentials and for the canonical
normal modes of the scalar-tensor action. Scalar, vector and tensor modes of
the geometry are classified according to four-dimensional Lorentz
transformations. While the tensor modes of the geometry live on the brane
determining the corrections to Newton law, the scalar and and vector
fluctuations exhibit non normalizable zero modes and are, consequently, not
localized on the brane. The spectrum of the massive modes of the fluctuations
is analyzed using supersymmetric quantum mechanics.Comment: 29 pages in Latex styl
Curvature Dependence of Running Gauge Coupling and Confinement in AdS/CFT Correspondence
We construct IIB supergravity (viewed as dilatonic gravity) background with
non-trivial dilaton and with curved four-dimensional space. Such a background
may describe another vacuum of maximally supersymmetric Yang-Mills theory or
strong coupling regime of (non)-supersymmetric gauge theory with (power-like)
running gauge coupling which depends on curvature. Curvature dependent
quark-antiquark potential is calculated where the geometry type of hyperbolic
(or de Sitter universe) shows (or not) the tendency of the confinement.
Generalization of IIB supergravity background with non-constant axion is
presented. Quark-antiquark potential being again curvature-dependent has a
possibility to produce the standard area law for large separations.Comment: LaTeX file, 24 pages, presentation is improve
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