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W. A. Sabra

Publications and source records attributed to W. A. Sabra.

At least 19 recordsLinked to original sources
arXiv2026

Single-Variable Solutions in Supergravity

We construct four families of spacetime metrics depending on a single variable for a broad class of $D$-dimensional gravitational theories coupled to scalar and Abelian gauge fields. As applications of the general formalism, we derive one-variable solutions of ungauged $\mathcal{N}=2$, $D=4$ supergravity coupled to vector multiplets. We also obtain explicit solutions for a consistent truncation of $\mathcal{N}=8$, $D=4$ supergravity, as well as for theories whose scalar fields parametrize the symmetric coset manifolds $SL(N,\mathbb{R})/SO(N,\mathbb{R})$. In all cases, the geometry of the scalar manifold plays a central role in determining the structure of the resulting solutions with nontrivial scalar and gauge field configurations.

hep-th↗
arXiv2025

Landau-Lifshitz Solutions of N=2, D=5 Supergravity

We study families of solutions depending only on one coordinate for the theories of N=2,five-dimensional supergravity coupled to vector multiplets. Four families of solutions, valid for all space-time signatures, are obtained. The explicit metrics of the solutions depend on the Jordan normal forms of constrained matrices. Examples with three charges are given for the so-called STU model.

hep-th↗
arXiv2025

One-variable Metrics in String Theory

Exact solutions depending on one variable of gravitational theory with antisymmetric tensor and a coupled dilaton field are obtained in arbitrary space-time dimensions. These solutions are relevant to M-theory, type IIA and type IIB supergravity theories in various space-time signatures.

hep-th↗
arXiv2024

Metrics depending on one variable in D-dimensional Einstein-Maxwell Theory

We present new families of solutions of D-dimensional Einstein-Maxwell theory depending on one variable for all space-time signatures. The solutions found can be thought of as generalized Melvin solutions including fluxtubes, domain walls and cosmological space-times. Explicit examples are given in four and five space-time dimensions.

gr-qc↗
arXiv2024

Real Supersymmetric Solutions of (3,2) Signature Five-Dimensional Supergravity

We classify supersymmetric solutions of D=5 (3,2) signature supergravity with either vanishing or imaginary gauge coupling constant preserving the minimal N=2 supersymmetry. We prove that the geometry of such solutions is characterized by a nilpotent integrable endomorphism, and obtain the necessary and sufficient conditions on the fluxes imposed by supersymmetry. We also construct examples of supersymmetric domain wall solutions for which the nilpotent integrable endomorphism is associated with a Killing-Yano 2-form, as well as a new descendant preon solution which preserves N=6 supersymmetry. This is notable as such N=6 descendant solutions do not exist in the standard signature D=5 supergravity.

hep-th↗
arXiv2023

Melvin Space-times in Supergravity

We consider Melvin-like cosmological and static solutions for the theories of ${\cal N}=2$, $D=4$ supergravity coupled to vector multiplets. We analyze the equations of motion and give some explicit solutions with one scalar and two gauge fields. Generalized Melvin solutions with four charges are also constructed for an embedding of a truncated ${\cal N}=8$ supergravity theory. Our results are then extended to supergravity theories with the scalar manifolds $SL(N, R)/SO(N, R)$. It is shown that solutions with $N$ charges only exist for $N=8$, $6$ and $5$ corresponding to theories with space-time dimensions $D=4$, $5$ and $7$.

hep-th↗
arXiv2022

Kasner Metrics and Very Special Geometry

We consider general charged Kasner-like solutions for the theory of five-dimensional supergravity coupled to Abelian vector multiplets in arbitrary space-time signature. These solutions, depending on the choice of coordinates, can be thought of as generalisations of Melvin/Rosen cosmologies, flux-branes and domain walls.

hep-th↗
arXiv2021

Flow Equations In Arbitrary Signature

We discuss general bosonic configurations of four-dimensional N=2 supergravity coupled to vector multiplets in (t,s) space-time. The supergravity theories with Euclidean and neutral signature are described by the so-called para-special Kähler geometry. For extremal solutions, we derive in a unified fashion, using the equations of motion, the flow equations for all space-time signatures. Demanding that the solutions with neutral and Euclidean signatures admit unbroken supersymmetry, we derive the constraints, known as the stabilisation equations, on the para-covariantly holomorphic sections expressed in terms of the adapted coordinates. The stabilisation equations expressed in terms of the para-complex sections imply generalised flow equations in terms of para-complex central charge. For Euclidean and neutral signature, it is demonstrated that solutions for either signs of gauge kinetic terms are mapped into each other via field redefinitions.

hep-th↗
arXiv2020

Neutral Signature Gauged Supergravity Solutions

We classify all supersymmetric solutions of minimal D=4 gauged supergravity with (2,2) signature and a positive cosmological constant which admit exactly one Killing spinor. This classification produces a geometric structure which is more general than that found for previous classifications of N=2 supersymmetric solutions of this theory. We illustrate how the N=2 solutions which consist of a fibration over a 3-dimensional Lorentzian Gauduchon-Tod base space can be written in terms of this more generic geometric structure.

hep-th↗
arXiv2020

Kasner Branes with Arbitrary Signature

We present static and time-dependent solutions for the theory of gravity with a dilaton field and an arbitrary rank antisymmetric tensor. The solutions constructed are valid for arbitrary space-time dimensions and signatures.

hep-th↗
arXiv2019

Real Killing Spinors in Neutral Signature

Spinorial geometry methods are used to classify solutions admitting Majorana Killing spinors of the minimal 4-dimensional supergravity in neutral signature, with vanishing cosmological constant and a single Maxwell field strength. Two classes of solutions preserving the minimal amount of supersymmetry are found. The first class admits a null-Kahler structure and corresponds to a class of self-dual solutions found by Bryant. The second class admits a null and rotation-free geodesic congruence with respect to which a parallel frame can be chosen. Examples of solutions in the former class are pseudo-hyper-Kahler manifolds; and examples in the latter class include self-dual solutions, as well as a neutral-signature IWP-type solution.

hep-th↗
arXiv2018

Solutions of D=4 Gauged Pseudo-Supergravity

The techniques of spinorial geometry are used to classify solutions admitting Killing spinors in the theory of minimal anti-de Sitter $N=2$, $D=4$ supergravity, where the gauge kinetic term comes with the opposite sign. There are four classes of solutions. One class is described by metrics corresponding to gravitational waves propagating on $AdS_2\times H^2$. The second class of solution is a new solution corresponding to a special limiting case of the Killing spinor. The third class of solution corresponds to fibrations over a Lorentzian three dimensional manifold which has a Lorentzian Gauduchon-Tod structure. The fourth class of solution is a cosmological extension of a Majumdar-Papapetrou type solution, described by a function satisfying the wave equation on $\mathbb{R}^{2,1}$ .

hep-th↗
arXiv2018

Solutions of Minimal Four Dimensional de Sitter Supergravity

Pseudo-supersymmetric solutions of minimal $N=2$, $D=4$ de Sitter supergravity are classified using spinorial geometry techniques. We find three classes of solutions. The first class of solution consists of geometries which are fibrations over a 3-dimensional manifold equipped with a Gauduchon-Tod structure. The second class of solution is the cosmological Majumdar-Papapetrou solution of Kastor and Traschen, and the third corresponds to gravitational waves propagating in the Nariai cosmology.

hep-th↗
arXiv2017

Special Geometry and Space-time Signature

We construct N=2 four and five-dimensional supergravity theories coupled to vector multiplets in various space-time signatures (t,s), where t and s refer, respectively, to the number of time and spatial dimensions. The five-dimensional supergravity theories, t+s=5, are constructed by investigating the integrability conditions arising from Killing spinor equations. The five-dimensional supergravity theories can also be obtained by reducing Hull's eleven-dimensional supergravities on a Calabi-Yau threefold. The dimensional reductions of the five-dimensional supergravities on space and time-like circles produce N=2 four-dimensional supergravity theories with signatures (t-1,s) and (t,s-1) exhibiting projective special (para)-Kähler geometry.

hep-th↗
arXiv2016

Euclidean Supergravity and Multi-Centered Solutions

In ungauged supergravity theories, the no-force condition for BPS states implies the existence of stable static multi-centered solutions. The first solutions to Einstein-Maxwell theory with a positive cosmological constant describing an arbitrary number of charged black holes were found by Kastor and Traschen. Generalisations to five and higher dimensional theories were obtained by London. Multi-centered solutions in gauged supergravity, even with time-dependence allowed, have yet to be constructed. In this letter we construct supersymmetry-preserving multi-centered solutions for the case of D=5, N=2 Euclidean gauged supergravity coupled to an arbitrary number of vector multiplets. Higher dimensional Einstein-Maxwell multi-centered solutions are also presented.

hep-th↗
arXiv2015

Phantom Metrics With Killing Spinors

We study metric solutions of Einstein-anti-Maxwell theory admitting Killing spinors. The analogue of the IWP metric which admits a space-like Killing vector is found and is expressed in terms of a complex function satisfying the wave equation in flat (2+1)-dimensional space-time. As examples, electric and magnetic Kasner spaces are constructed by allowing the solution to depend only on the time coordinate. Euclidean solutions are also presented.

hep-th↗
arXiv2015

Index Theory and Supersymmetry of 5D Horizons

We prove that the near-horizon geometries of minimal gauged five-dimensional supergravity preserve at least half of the supersymmetry. If the near-horizon geometries preserve a larger fraction, then they are locally isometric to $AdS_5$. Our proof is based on Lichnerowicz type theorems for two horizon Dirac operators constructed from the supercovariant connection restricted to the horizon sections, and on an application of the index theorem. An application is that all half-supersymmetric five-dimensional horizons admit an $\mathfrak{sl}(2, {\mathbb{R}})$ symmetry subalgebra.

hep-th↗