894 research outputs found
Two-Centered Magical Charge Orbits
We determine the two-centered generic charge orbits of magical N = 2 and
maximal N = 8 supergravity theories in four dimensions. These orbits are
classified by seven U-duality invariant polynomials, which group together into
four invariants under the horizontal symmetry group SL(2,R). These latter are
expected to disentangle different physical properties of the two-centered
black-hole system. The invariant with the lowest degree in charges is the
symplectic product (Q1,Q2), known to control the mutual non-locality of the two
centers.Comment: 1+17 pages, 1 Table; v2: Eq. (3.23) corrected; v3: various
refinements in text and formulae, caption of Table 1 expanded, Footnote and
Refs. added. To appear on JHE
First-order flows and stabilisation equations for non-BPS extremal black holes
We derive a generalised form of flow equations for extremal static and
rotating non-BPS black holes in four-dimensional ungauged N = 2 supergravity
coupled to vector multiplets. For particular charge vectors, we give
stabilisation equations for the scalars, analogous to the BPS case, describing
full known solutions. Based on this, we propose a generic ansatz for the
stabilisation equations, which surprisingly includes ratios of harmonic
functions.Comment: 27 pages; v2: presentation improved and references added as in the
published versio
Black holes in supergravity and integrability
Stationary black holes of massless supergravity theories are described by
certain geodesic curves on the target space that is obtained after dimensional
reduction over time. When the target space is a symmetric coset space we make
use of the group-theoretical structure to prove that the second order geodesic
equations are integrable in the sense of Liouville, by explicitly constructing
the correct amount of Hamiltonians in involution. This implies that the
Hamilton-Jacobi formalism can be applied, which proves that all such black hole
solutions, including non-extremal solutions, possess a description in terms of
a (fake) superpotential. Furthermore, we improve the existing integration
method by the construction of a Lax integration algorithm that integrates the
second order equations in one step instead of the usual two step procedure. We
illustrate this technology with a specific example.Comment: 44 pages, small typos correcte
T-duality and closed string non-commutative (doubled) geometry
We provide some evidence that closed string coordinates will become
non-commutative turning on H-field flux background in closed string
compactifications. This is in analogy to open string non-commutativity on the
world volume of D-branes with B- and F-field background. The class of
3-dimensional backgrounds we are studying are twisted tori (fibrations of a
2-torus over a circle) and the their T-dual H-field, 3-form flux backgrounds
(T-folds). The spatial non-commutativity arises due to the non-trivial
monodromies of the toroidal Kahler resp. complex structure moduli fields, when
going around the closed string along the circle direction. In addition we study
closed string non-commutativity in the context of doubled geometry, where we
argue that in general a non-commutative closed string background is T-dual to a
commutative closed string background and vice versa. Finally, in analogy to
open string boundary conditions, we also argue that closed string momentum and
winding modes define in some sense D-branes in closed string doubled geometry.Comment: 31 pages, references added, extended version contains new sections
3.3., 3.4 and
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
Heterotic Sigma Models with N=2 Space-Time Supersymmetry
We study the non-linear sigma model realization of a heterotic vacuum with
N=2 space-time supersymmetry. We examine the requirements of (0,2) + (0,4)
world-sheet supersymmetry and show that a geometric vacuum must be described by
a principal two-torus bundle over a K3 manifold.Comment: 20 pages, uses xy-pic; v3: typos corrected, reference added,
discussion of constraints on Hermitian form modifie
Black holes and black strings of N=2, d=5 supergravity in the H-FGK formalism
We study general classes and properties of extremal and non-extremal static
black-hole solutions of N=2, d=5 supergravity coupled to vector multiplets
using the recently proposed H-FGK formalism, which we also extend to static
black strings. We explain how to determine the integration constants and
physical parameters of the black-hole and black-string solutions. We derive
some model-independent statements, including the transformation of non-extremal
flow equations to the form of those for the extremal flow. We apply our methods
to the construction of example solutions (among others a new extremal string
solution of heterotic string theory on K_3 \times S^1). In the cases where we
have calculated it explicitly, the product of areas of the inner and outer
horizon of a non-extremal solution coincides with the square of the
moduli-independent area of the horizon of the extremal solution with the same
charges.Comment: 33 pages. Revised version: references added. No other change
M-theory moduli spaces and torsion-free structures
Motivated by the description of M-theory compactifications to
four-dimensions given by Exceptional Generalized Geometry, we propose a way to
geometrize the M-theory fluxes by appropriately relating the compactification
space to a higher-dimensional manifold equipped with a torsion-free structure.
As a non-trivial example of this proposal, we construct a bijection from the
set of -structures on an eight-dimensional -bundle to the set
of -structures on the base space, fully characterizing the
-torsion clases when the total space is equipped with a torsion-free
-structure. Finally, we elaborate on how the higher-dimensional
manifold and its moduli space of torsion-free structures can be used to obtain
information about the moduli space of M-theory compactifications.Comment: 24 pages. Typos fixed. Minor clarifications adde
D=7 / D=6 Heterotic Supergravity with Gauged R-Symmetry
We construct a family of chiral anomaly-free supergravity theories in D=6
starting from D=7 supergravity with a gauged noncompact R-symmetry, employing a
Horava-Witten bulk-plus-boundary construction. The gauged noncompact R-symmetry
yields a positive (de Sitter sign) D=6 scalar field potential. Classical
anomaly inflow which is needed to cancel boundary-field loop anomalies requires
careful consideration of the gravitational, gauge, mixed and local
supersymmetry anomalies. Coupling of boundary hypermultiplets requires care
with the Sp(1) gauge connection required to obtain quaternionic Kahler target
manifolds in D=6. This class of gauged R-symmetry models may be of use as
starting points for further compactifications to D=4 that take advantage of the
positive scalar potential, such as those proposed in the scenario of
supersymmetry in large extra dimensions.Comment: 43 pages, plain Latex; Clarification of discussion and references
adde
Massless D-strings and moduli stabilization in type I cosmology
We consider the cosmological evolution induced by the free energy F of a gas
of maximally supersymmetric heterotic strings at finite temperature and weak
coupling in dimension D>=4. We show that F, which plays the role of an
effective potential, has minima associated to enhanced gauge symmetries, where
all internal moduli can be attracted and dynamically stabilized. Using the fact
that the heterotic/type I S-duality remains valid at finite temperature and can
be applied at each instant of a quasi-static evolution, we find in the dual
type I cosmology that all internal NS-NS and RR moduli in the closed string
sector and the Wilson lines in the open string sector can be stabilized. For
the special case of D=6, the internal volume modulus remains a flat direction,
while the dilaton is stabilized. An essential role is played by light D-string
modes wrapping the internal manifold and whose contribution to the free energy
cannot be omitted, even when the type I string is at weak coupling. As a
result, the order of magnitude of the internal radii expectation values on the
type I side is (lambda_I alpha')^{1/2}, where lambda_I is the ten-dimensional
string coupling. The non-perturbative corrections to the type I free energy can
alternatively be described as effects of "thermal E1-instantons", whose
worldsheets wrap the compact Euclidean time cycle.Comment: 39 pages, 1 figur
- …