433 research outputs found
Superpotentials from flux compactifications of M-theory
In flux compactifications of M-theory a superpotential is generated whose
explicit form depends on the structure group of the 7-dimensional internal
manifold. In this note, we discuss superpotentials for the structure groups:
G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For
SU(3) structures, the non-zero flux components entering the superpotential
describe an effective 1-dimensional model and a Chern-Simons model if there are
SU(2) structures.Comment: 10 page
Entropy of N=2 black holes and their M-brane description
In this paper we discuss the M-brane description for a N=2 black hole. This
solution is a result of the compactification of M-5-brane configurations over a
Calabi-Yau threefold with arbitrary intersection numbers . In analogy
to the D-brane description where one counts open string states we count here
open 2-branes which end on the M-5-brane.Comment: 12 pages, (hyper) LaTeX, (minor changes and refs. added
Fluxes in M-theory on 7-manifolds and G structures
We consider warp compactifications of M-theory on 7-manifolds in the presence
of 4-form fluxes and investigate the constraints imposed by supersymmetry. As
long as the 7-manifold supports only one Killing spinor we infer from the
Killing spinor equations that non-trivial 4-form fluxes will necessarily curve
the external 4-dimensional space. On the other hand, if the 7-manifold has at
least two Killing spinors, there is a non-trivial Killing vector yielding a
reduction of the 7-manifold to a 6-manifold and we confirm that 4-form fluxes
can be incorporated if one includes non-trivial SU(3) structures.Comment: 13 pages, Latex; minor changes & add reference
Towards Quantum Cosmology without Singularities
In this paper we investigate the vanishing of cosmological singularities by
quantization. Starting from a 5d Kaluza--Klein approach we quantize, as a first
step, the non--spherical metric part and the dilaton field. These fields which
are classically singular become smooth after quantization. In addition, we
argue that the incorporation of non perturbative quantum corrections form a
dilaton potential. Technically, the procedure corresponds to the quantization
of 2d dilaton gravity and we discuss several models. From the 4d point of view
this procedure is a semiclassical approach where only the dilaton and moduli
matter fields are quantized.Comment: 9 pages, 2 figures, Latex, epsfig.sty, epsf.te
Bent BPS domain walls of D=5 N=2 gauged supergravity coupled to hypermultiplets
Within D=5 N=2 gauged supergravity coupled to hypermultiplets we derive
consistency conditions for BPS domain walls with constant negative curvature on
the wall. For such wall solutions to exist, the covariant derivative of the
projector, governing the constraint on the Killing spinor, has to be non-zero
and proportional to the cosmological constant on the domain walls. We also
prove that in this case solutions of the Killing spinor equations are solutions
of the equations of motion. We present explicit, analytically solved examples
of such domain walls, employing the universal hypermultiplet fields. These
examples involve the running of two scalar fields and the space-time in the
transverse direction that is cut off at a critical distance, governed by the
magnitude of the negative cosmological constant on the wall.Comment: 18 pages, Late
General N = 1 Supersymmetric Flux Vacua of (Massive) Type IIA String Theory
We derive conditions for the existence of four-dimensional \N=1
supersymmetric flux vacua of massive type IIA string theory with general
supergravity fluxes turned on. For an SU(3) singlet Killing spinor, we show
that such flux vacua exist only when the internal geometry is nearly-K\"ahler.
The geometry is not warped, all the allowed fluxes are proportional to the mass
parameter and the dilaton is fixed by a ratio of (quantized) fluxes. The
four-dimensional cosmological constant, while negative, becomes small in the
vacuum with the weak string coupling.Comment: 4 page
Time-dependent backgrounds from supergravity with gauged non-compact R-symmetry
We obtain a general class of time-dependent, asymptotically de Sitter
backgrounds which solve the first order bosonic equations that extremize the
action for supergravity with gauged non-compact -symmetry. These backgrounds
correspond only to neutral fields with the correct sign of kinetic energy.
Within N=2 five-dimensional supergravity with vector-superfields we provide
examples of multi-centered charged black holes in asymptotic de Sitter space,
whose spatial part is given by a time-dependent hyper-K\"ahler space. Reducing
these backgrounds to four dimensions yields asymptotically de Sitter
multi-centered charged black hole backgrounds and we show that they are related
to an instanton configuration by a massive T-duality over time. Within N=2
gauged supergravity in four (and five)-dimensions with hyper-multiplets there
could also be neutral cosmological backgrounds that are regular and correspond
to the different de Sitter spaces at early and late times.Comment: 28 pages, Latex; minor changes and add reference
De Sitter vacua from N=2 gauged supergravity
Typical de Sitter (dS) vacua of gauged supergravity correspond to saddle
points of the potential and often the unstable mode runs into a singularity. We
explore the possibility to obtain dS points where the unstable mode goes on
both sides into a supersymmetric smooth vacuum. Within N=2 gauged supergravity
coupled to the universal hypermultiplet, we have found a potential which has
two supersymmetric minima (one of them can be flat) and these are connected by
a de Sitter saddle point. In order to obtain this potential by an Abelian
gauging, it was important to include the recently proposed quantum corrections
to the universal hypermultiplet sector. Our results apply to four as well as
five dimensional gauged supergravity theories.Comment: 25 pages, 1 figure, add refs and corrected typo
Curved BPS domain walls and RG flow in five dimensions
We determine, in the context of five-dimensional gauged
supergravity with vector and hypermultiplets, the conditions under which curved
(non Ricci flat) supersymmetric domain wall solutions may exist. These curved
BPS domain wall solutions may, in general, be supported by non-constant vector
and hyper scalar fields. We establish our results by a careful analysis of the
BPS equations as well as of the associated integrability conditions and the
equations of motion. We construct an example of a curved BPS solution in a
gauged supergravity model with one hypermultiplet. We also discuss the dual
description of curved BPS domain walls in terms of RG flows.Comment: 18 pages, LaTeX, 5 figures; added reference
BPS equations in N=2, D=5 supergravity with hypermultiplets
With the general aim to classify BPS solutions in N=2, D=5 supergravities
interacting with an arbitrary number of vector, tensor and hypermultiplets,
here we begin considering the most general electrostatic, spherical-symmetric
BPS solutions in the presence of hypermultiplet couplings. We discuss the
properties of the BPS equations and the restrictions imposed by their
integrability conditions. We exhibit explicit solutions for the case of static
BPS black-holes coupled to one (the so called universal) hypermultiplet.Comment: 20 pages, v3 some corrections performed; we thank A.Van Proeyen for
the pointing ou
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