387 research outputs found

### N=8 BPS black holes preserving 1/8 supersymmetry

In the context of N=8 supergravity we consider BPS black-holes that preserve
1/8 supersymmetry. It was shown in a previous paper that, modulo U-duality
transformations of E_{7(7)} the most general solution of this type can be
reduced to a black-hole of the STU model. In this paper we analize this
solution in detail, considering in particular its embedding in one of the
possible Special K\"ahler manifold compatible with the consistent truncations
to N=2 supergravity, this manifold being the moduli space of the T^6/Z^3
orbifold, that is: SU(3,3)/SU(3)*U(3). This construction requires a crucial use
of the Solvable Lie Algebra formalism. Once the group-theoretical analisys is
done, starting from a static, spherically symmetric ans\"atz, we find an exact
solution for all the scalars (both dilaton and axion-like) and for gauge
fields, together with their already known charge-dependent fixed values, which
yield a U-duality invariant entropy. We give also a complete translation
dictionary between the Solvable Lie Algebra and the Special K\"ahler formalisms
in order to let comparison with other papers on similar issues being more
immediate. Although the explicit solution is given in a simplified case where
the equations turn out to be more manageable, it encodes all the features of
the more general one, namely it has non-vanishing entropy and the scalar fields
have a non-trivial radial dependence.Comment: 29+1 pages, 1 Latex file; a misprint in the entropy formula,
eq.(5.14), correcte

### Minimal $D=7$ Supergravity and the supersymmetry of Arnold-Beltrami Flux branes

In this paper we study some properties of the newly found Arnold-Beltrami
flux-brane solutions to the minimal $D=7$ supergravity. To this end we first
single out the appropriate Free Differential Algebra containing both a gauge
$3$-form $\mathbf{B}^{[3]}$ and a gauge $2$-form $\mathbf{B}^{[2]}$: then we
present the complete rheonomic parametrization of all the generalized
curvatures. This allows us to identify two-brane configurations with
Arnold-Beltrami fluxes in the transverse space with exact solutions of
supergravity and to analyze the Killing spinor equation in their background. We
find that there is no preserved supersymmetry if there are no additional
translational Killing vectors. Guided by this principle we explicitly construct
Arnold-Beltrami flux two-branes that preserve $0$, $1/8$ and $1/4$ of the
original supersymmetry. Two-branes without fluxes are instead BPS states and
preserve $1/2$ supersymmetry. For each two-brane solution we carefully study
its discrete symmetry that is always given by some appropriate crystallographic
group $\Gamma$. Such symmetry groups $\Gamma$ are transmitted to the $D=3$
gauge theories on the brane world--volume that occur in the gauge/gravity
correspondence. Furthermore we illustrate the intriguing relation between gauge
fluxes in two-brane solutions and hyperinstantons in $D=4$ topological
sigma-models.Comment: 56 pages, LaTeX source, 8 jpg figures, typos correcte

### Pure Spinor Superstrings on Generic type IIA Supergravity Backgrounds

We derive the Free Differential Algebra for type IIA supergravity in 10
dimensions in the string frame. We provide all fermionic terms for all
curvatures. We derive the Green-Schwarz sigma model for type IIA superstring
based on the FDA construction and we check its invariance under kappa-symmetry.
Finally, we derive the pure spinor sigma model and we check the BRST
invariance. The present derivation has the advantage that the resulting sigma
model is constructed in terms of the superfields appearing in the FDA and
therefore one can directly relate a supergravity background with the
corresponding sigma model. The complete explicit form of the BRST
transformations is given and some new pure spinor constraints are obtained.
Finally, the explicit form of the action is given.Comment: 31 pp. no figures, latex, some modifications at pag 21, a missing
term in 4.51 corrected. Discussion on BRST symmetry improve

### Partial N=2 --> N=1 Local Supersymmetry Breaking and Solvable Lie Algebras

Generic partial supersymmetry breaking of N=2 supergravity with zero vacuum
energy and with surviving unbroken arbitrary gauge groups is exhibited.
Specific examples are given.Comment: 5 pages, 1 LaTeX-style file, 1 TeX, 2 Postscript figures. Seminar
given at the Work-Shop on "Gauge Theories, Applied Supersymmetry and Quantum
Gravity", Imperial College, London, 5-10 July 199

### D-branes, Orientifolds and K-theory

The complete D-brane spectrum in ZZ[squared] orientifolds is computed. Stable non-BPS D-branes with both integral and torsion charges are found. The relation to K-theory is discussed and a new K-theory relevant to orientifolds is suggested

### R-Symmetry and the Topological Twist of N=2 Effective Supergravities of Heterotic Strings

We discuss R-symmetries in locally supersymmetric N=2 gauge theories coupled
to hypermultiplets which can be thought of as effective theories of heterotic
superstring models. In this type of supergravities a suitable R-symmetry exists
and can be used to topologically twist the theory: the vector multiplet
containing the dilaton-axion field has different R-charge assignments with
respect to the other vector multiplets. Correspondingly a system of coupled
instanton equations emerges, mixing gravitational and Yang--Mills instantons
with triholomorphic hyperinstantons and axion-instantons. For the tree-level
classical special manifolds $ST(n)=SU(1,1)/U(1)\times SO(2,n)/(SO(2)$ $\times
SO(n))$ R-symmetry with the specified properties is a continuous symmetry, but
for the quantum corrected manifolds ${\hat {ST}}(n)$ a discrete R--group of
electric--magnetic duality rotations is sufficient and we argue that it exists.Comment: 40 pages, plain LaTeX. Final version to appear on IJMP

### Black hole - D-brane correspondence: An example

We explore the connection between D-branes and black holes in one particular
case: a $D3$-brane compactified to four dimensions on $T^6/Z_3$. Using the
$D$-brane boundary state description we show the equivalence with a double
extremal N=2 black hole solution of four dimensional supergravity.Comment: 15 pages, LaTeX. Contribution by C. Nunez to the conference Quantum
Gravity in the Southern Cone, Bariloche 7-10 January 1998; to appear in the
proceeding

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