9 research outputs found
Axion-Dilaton Domain Walls and Fake Supergravity
Dynamical systems methods are used to investigate domain-wall solutions of a
two-parameter family of models in which gravity is coupled to an axion, and to
a dilaton with an exponential potential of either sign. A complete global
analysis is presented for (i) constant axion and (ii) flat walls, including a
study of bifurcations and a new exact domain-wall solution with non-constant
axion. We reconsider `fake supergravity' issues in light of these results. We
show, by example, how domain walls determine multi-valued superpotentials that
branch at stationary points that are not stationary points of the potential,
and we apply this result to potentials with anti-de Sitter vacua. We also show
by example that `adapted' truncation to a single-scalar model is sometimes
inconsistent, and we propose a `generalized' fake supergravity formalism that
applies in some such cases.Comment: 43pp, 19 figures; minor corrections and extensions; one additional
figur
From Wave Geometry to Fake Supergravity
The `Wave Geometry' equation of the pre-WWII Hiroshima program is also the
key equation of the current `fake supergravity' program. I review the status of
(fake) supersymmetric domain walls and (fake) pseudo-supersymmetric
cosmologies. An extension of the domain-wall/cosmology correspondence to a
triple correspondence with instantons shows that `pseudo-supersymmetry' has
another interpretation as Euclidean supersymmetry.Comment: 14 pages. Minor Revisions to original. To appear in proceedings of
the 5th International Symposium on Quantum Theory and Symmetries (QTS5),
Vallodolid, July 2007. in version
Dilaton Domain Walls and Dynamical Systems
Domain wall solutions of -dimensional gravity coupled to a dilaton field
with an exponential potential are shown
to be governed by an autonomous dynamical system, with a transcritical
bifurcation as a function of the parameter when . All
phase-plane trajectories are found exactly for , including
separatrices corresponding to walls that interpolate between and
adS_{d-1} \times\bR, and the exact solution is found for . Janus-type
solutions are interpreted as marginal bound states of these ``separatrix
walls''. All flat domain wall solutions, which are given exactly for any
, are shown to be supersymmetric for some superpotential ,
determined by the solution.Comment: 30 pp, 11 figs, significant revision of original. Minor additional
corrections in version to appear in journa
Scaling Cosmologies of N=8 Gauged Supergravity
We construct exact cosmological scaling solutions in N=8 gauged supergravity.
We restrict to solutions for which the scalar fields trace out geodesic curves
on the scalar manifold. Under these restrictions it is shown that the axionic
scalars are necessarily constant. The potential is then a sum of exponentials
and has a very specific form that allows for scaling solutions. The scaling
solutions describe eternal accelerating and decelerating power-law universes,
which are all unstable. An uplift of the solutions to 11-dimensional
supergravity is carried out and the resulting timedependent geometries are
discussed. In the discussion we briefly comment on the fact that N=2 gauged
supergravity allows stable scaling solutions.Comment: 17 pages; referenced added, reportnr changed and some corrections in
section
Axion-Dilaton Cosmology and Dark Energy
We discuss a class of flat FRW cosmological models based on D=4 axion-dilaton
gravity universally coupled to cosmological background fluids. In particular,
we investigate the possibility of recurrent acceleration, which was recently
shown to be generically realized in a wide class of axion-dilaton models, but
in absence of cosmological background fluids. We observe that, once we impose
the existence of radiation -and matter- dominated earlier stages of cosmic
evolution, the axion-dilaton dynamics is altered significantly with respect to
the case of pure axion-dilaton gravity. During the matter dominated epoch the
scalar fields remain either frozen, due to the large expansion rate, or enter a
cosmological scaling regime. In both cases, oscillations of the effective
equation of state around the acceleration boundary value are impossible. Models
which enter an oscillatory stage in the low redshift regime, on the other hand,
are disfavored by observations. We also comment on the viability of the
axion-dilaton system as a candidate for dynamical dark energy. In a certain
subclass of models, an intermediate scaling regime is succeeded by eternal
acceleration. We also briefly discuss the issue of dependence on initial
conditions.Comment: 28 pages, 11 figure
Fake supersymmetry versus Hamilton-Jacobi
We explain when the first-order Hamilton-Jacobi equations for black holes
(and domain walls) in (gauged) supergravity, reduce to the usual first-order
equations derived from a fake superpotential. This turns out to be equivalent
to the vanishing of a newly found constant of motion and we illustrate this
with various examples. We show that fake supersymmetry is a necessary condition
for having physically sensible extremal black hole solutions. We furthermore
observe that small black holes become scaling solutions near the horizon. When
combined with fake supersymmetry, this leads to a precise extension of the
attractor mechanism to small black holes: The attractor solution is such that
the scalars move on specific curves, determined by the black hole charges, that
are purely geodesic, although there is a non-zero potential.Comment: 20 pages, v2: Typos corrected, references adde