arXiv subjects

Wafic A. Sabra

Publications and source records attributed to Wafic A. Sabra.

18 recordsLinked to original sources

arXiv2018

Spinorial geometry, off-shell Killing spinor identities and higher derivative 5D supergravities

Killing spinor identities relate components of equations of motion to each other for supersymmetric backgrounds. The only input required is the field content and the supersymmetry transformations of the fields, as long as an on-shell supersymmetrization of the action without additional fields exists. If we consider off-shell supersymmetry it is clear that the same relations will occur between components of the equations of motion independently of the specific action considered, in particular the Killing spinor identities can be derived for arbitrary, including higher derivative, supergravities, with a specified matter content. We give the Killing spinor identities for five-dimensional $\mathcal{N}=2$ ungauged supergravities coupled to Abelian vector multiplets, and then using spinorial geometry techniques so that we have explicit representatives for the spinors, we discuss the particular case of the time-like class of solutions to theories with perturbative corrections at the four derivative level. We also discuss the maximally supersymmetric solutions in the general off-shell case.

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arXiv2016

Euclidean Supergravity in Five Dimensions

We construct a 5D, N = 2 Euclidean theory of supergravity coupled to vector multiplets. Upon reducing this theory over a circle we recover the action of 4D, N = 2 Euclidean supergravity coupled to vector multiplets.

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arXiv2015

Phantom Space-times in Fake Supergravity

We discuss phantom metrics admitting Killing spinors in fake N=2, D=4 supergravity coupled to vector multiplets. The Abelian U(1) gauge fields in the fake theory have kinetic terms with the wrong sign. We solve the Killing spinor equations for the standard and fake theories in a unified fashion by introducing a parameter which distinguishes between the two theories. The solutions found are fully determined in terms of algebraic conditions, the so-called stabilisation equations, in which the symplectic sections are related to a set of functions. These functions are harmonic in the case of the standard supergravity theory and satisfy the wave-equation in flat (2+1)-space-time in the fake theory. Explicit examples are given for the minimal models with quadratic prepotentials.

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arXiv2015

On Non-extremal Instantons and Black Holes

We consider a general analysis and a specific ansatz for the study of non-supersymmetric solutions in arbitrary dimensions and various metric signatures. In all cases, we find that the conditions on the solutions can be written in terms of quadratic forms involving the gauge coupling of the theory and constants of integration associated with the scalar fields. Depending on the signature of the metric, our analysis should provide a general framework for finding non-extremal black holes, instantons, branes and S-branes.

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arXiv2014

No Fermionic Wigs for BPS Attractors in 5 Dimensions

We analyze the fermionic wigging of 1/2-BPS (electric) extremal black hole attractors in N=2, D=5 ungauged Maxwell-Einstein supergravity theories, by exploiting anti-Killing spinors supersymmetry transformations. Regardless of the specific data of the real special geometry of the manifold defining the scalars of the vector multiplets, and differently from the D=4 case, we find that there are no corrections for the near--horizon attractor value of the scalar fields; an analogous result also holds for 1/2-BPS (magnetic) extremal black string. Thus, the attractor mechanism receives no fermionic corrections in D=5 (at least in the BPS sector).

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arXiv2009

Gauduchon-Tod structures, Sim holonomy and De Sitter supergravity

Solutions of five-dimensional De Sitter supergravity admitting Killing spinors are considered, using spinorial geometry techniques. It is shown that the "null" solutions are defined in terms of a one parameter family of 3-dimensional constrained Einstein-Weyl spaces called Gauduchon-Tod structures. They admit a geodesic, expansion-free, twist-free and shear-free null vector field and therefore are a particular type of Kundt geometry. When the Gauduchon-Tod structure reduces to the 3-sphere, the null vector becomes recurrent, and therefore the holonomy is contained in Sim(3), the maximal proper subgroup of the Lorentz group SO(4,1). For these geometries, all scalar invariants built from the curvature are constant. Explicit examples are discussed.

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arXiv2008

Isometries of Half Supersymmetric Time-Like Solutions In Five Dimensions

Spinorial geometry techniques have recently been used to classify all half supersymmetric solutions in gauged five dimensional supergravity with vector multiplets. In this paper we consider solutions for which at least one of the Killing spinors generates a timelike Killing vector. We obtain coordinate transformations which considerably simplify the solutions, and in a number of cases, we obtain explicitly some additional Killing vectors which were hidden in the original analysis.

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arXiv2008

Hamilton-Jacobi Counterterms for Einstein-Gauss-Bonnet Gravity

The on-shell gravitational action and the boundary stress tensor are essential ingredients in the study of black hole thermodynamics. We employ the Hamilton-Jacobi method to calculate the boundary counterterms necessary to remove the divergences and allow the study of the thermodynamics of Einstein-Gauss-Bonnet black holes.

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arXiv2007

Half-Supersymmetric Solutions in Five-Dimensional Supergravity

We present a systematic classification of half-supersymmetric solutions of gauged N=2, D=5 supergravity coupled to an arbitrary number of abelian vector multiplets for which at least one of the Killing spinors generate a time-like Killing vector.

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arXiv2007

Maximally Minimal Preons in Four Dimensions

Killing spinors of N=2, D=4 supergravity are examined using the spinorial geometry method, in which spinors are written as differential forms. By making use of methods developed in hep-th/0606049 to analyze preons in type IIB supergravity, we show that there are no simply connected solutions preserving exactly 3/4 of the supersymmetry.

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arXiv2006

Non-Supersymmetric Charged Domain Walls

We present general non-supersymmtric domain wall solutions with non-trivial scalar and gauge fields for gauged five-dimensional N=2 supergravity coupled to abelian vector multiplets.

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arXiv2003

Supersymmetric Domain Walls and Strings in D=5 gauged Supergravity coupled to Vector Multiplets

We present new supersymmetric domain wall and string solutions of five-dimensional N = 2 gauged supergravity coupled to an arbitrary number of vector multiplets. Using the techniques of very special geometry allows to obtain the most general domain wall preserving half of the supersymmetries. This solution, which describes a renormalization group flow in the dual field theory, is given in terms of Weierstrass elliptic functions. The magnetically charged, one quarter supersymmetric string solutions are shown to be closely related to Liouville theory. We furthermore investigate general product space compactifications, and show that topological transitions from AdS_3 x S^2 to AdS_3 x H^2 can occur when one moves in moduli space.

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arXiv2001

A Supersymmetric Solution in N=2 Gauged Supergravity with the Universal Hypermultiplet

We present supersymmetric solutions for the theory of gauged supergravity in five dimensions obtained by gauging the shift symmetry of the axion of the universal hypermultiplet. This gauged theory can also be obtained by dimensionally reducing M-theory on a Calabi-Yau threefold with background flux. The solution found preserves half of the N=2 supersymmetry, carries electric fields and has nontrivial scalar field representing the CY-volume. We comment on the possible solutions of more general hypermultiplet gauging.

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arXiv1998

Black Holes and Flop Transitions in M-Theory on Calabi-Yau Threefolds

We present fivedimensional extreme black hole solutions of M-theory compactified on Calabi-Yau threefolds and study these solutions in the context of flop transitions in the extended Kahler cone. In particular we consider a specific model and present black hole solutions, breaking half of N=2 supersymmetry, in two regions of the extended Kahler cone, which are connected by a flop transition. The conditions necessary to match both solutions at the flop transition are analysed. Finally we also discuss the conditions to obtain massless black holes at the flop transition.

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arXiv1998

Higher-Order Black-Hole Solutions in N=2 Supergravity and Calabi-Yau String Backgrounds

Based on special geometry, we consider corrections to N=2 extremal black-hole solutions and their entropies originating from higher-order derivative terms in N=2 supergravity. These corrections are described by a holomorphic function, and the higher-order black-hole solutions can be expressed in terms of symplectic Sp(2$n$+2) vectors. We apply the formalism to N=2 type-IIA Calabi-Yau string compactifications and compare our results to recent related results in the literature.

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arXiv1997

The entropy of near-extreme N=2 black holes

We give an explicit form of the classical entropy for four-dimensional static near-BPS-saturated black holes of generic N=2 superstring vacua. The expression is obtained by determining the leading corrections in the non-extremality parameter to the corresponding BPS-saturated black hole solutions. These classical results are quantitatively compared with the microscopic leading order corrections to the microscopic result of Maldacena Strominger and Witten for N=2 BPS-saturated black holes.

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arXiv1997

Moving Moduli, Calabi-Yau Phase Transitions and Massless BPS Configurations in Type II Superstrings

In this paper we discuss compactifications of type II superstrings where the moduli of the internal Calabi-Yau space vary over four-dimensional space time. The corresponding solutions of four-dimensional N=2 supergravity are given by charged, extremal BPS black hole configurations with non-constant scalar field values. In particular we investigate the behaviour of our solutions near those points in the Calabi-Yau moduli space where some internal cycles collapse and topology change (flop transitions, conifold transitions) can take place. The singular loci in the internal space are related to special points in the uncompactified space. The phase transition can happen either at spatial infinity (for positive charges) or on spheres (with at least one negative charge). The corresponding BPS configuration has zero ADM mass and can be regarded as a domain wall that separates topologically different vacua of the theory.

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arXiv1996

Duality Invariant Magnetohydrodynamics And Dyons

The theory of magnetohydrodynamics is extended to the cases of a plasma of separate magnetic and electric charges, as well as to a plasma of dyons respectively. In both these cases the system possesses electric-magnetic duality symmetry. In the former case we find that because of the existence of two independent generalized Ohm's law equations, the limit of infinite electric and magnetic conductivity results in the vanishing of both electric and magnetic fields, as well as the corresponding currents. In the dyonic case, we find that the resulting duality-invariant system of equations are equivalent to those of ordinary MHD, after suitable field redefinitions.

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