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Tomas Ortin

Publications and source records attributed to Tomas Ortin.

At least 73 records · Page 4Linked to original sources
arXiv2006

Seven-branes and Supersymmetry

We re-investigate the construction of half-supersymmetric 7-brane solutions of IIB supergravity. Our method is based on the requirement of having globally well-defined Killing spinors and the inclusion of SL(2,Z)-invariant source terms. In addition to the well-known solutions going back to Greene, Shapere, Vafa and Yau we find new supersymmetric configurations, containing objects whose monodromies are not related to the monodromy of a D7-brane by an SL(2,Z) transformation.

hep-th↗
arXiv2006

Supersymmetry, attractors and cosmic censorship

We show that requiring unbroken supersymmetry everywhere in black-hole-type solutions of N=2,d=4 supergravity coupled to vector supermultiplets ensures in most cases absence of naked singularities. We formulate three specific conditions which we argue are equivalent to the requirement of global supersymmetry. These three conditions can be related to absence of sources of NUT charge, angular momentum, scalar hair and negative energy, although the solutions can still have globally defined angular momentum and non-trivial scalar fields, as we show in an explicit example. Furthermore, only the solutions satisfying these requirements seem to have a microscopic interpretation in String Theory since only they have supersymmetric sources. These conditions exclude, for instance, singular solutions such as the Kerr-Newman with M=|q|, which fails to be everywhere supersymmetric. We also present a re-derivation of several results concerning attractors in N=2,d=4 theories based in the explicit knowledge of the most general solutions of the timelike class.

hep-th↗
arXiv2006

IIB Nine-branes

We calculate the tensions of all half-supersymmetric nine-branes in IIB string theory. In particular, we point out the existence of a solitonic IIB nine-brane. We find that the D9-brane and its duality transformations parametrize a two-dimensional surface in a four-dimensional space.

hep-th↗
arXiv2006

IIA Ten-forms and the Gauge Algebras of Maximal Supergravity Theories

We show that IIA supergravity can be extended with two independent 10-form potentials. These give rise to a single BPS IIA 9-brane. We investigate the bosonic gauge algebra of both IIA and IIB supergravity in the presence of 10-form potentials and point out an intriguing relation with the symmetry algebra $E_{11}$, which has been conjectured to be the underlying symmetry of string theory/M-theory.

hep-th↗
arXiv2006

Supersymmetric solutions of N=2 d=4 sugra: the whole ungauged shebang

In this article we complete the classification of the supersymmetric solutions of N=2 D=4 ungauged supergravity coupled to an arbitrary number of vector- and hypermultiplets. We find that in the timelike case the hypermultiplets cause the constant-time hypersurfaces to be curved and have su(2) holonomy identical to that of the hyperscalar manifold. The solutions have the same structure as without hypermultiplets but now depend on functions which are harmonic in the curved 3-dimensional space. We discuss an example obtained from a hyper-less solution via the c-map. In the null case we find that the hyperscalars can only depend on the null coordinate and the solutions are essentially those of the hyper-less case.

hep-th↗
arXiv2006

Supersymmetry and the Supergravity Landscape

In the recent times a lot of effort has been devoted to improve our knowledge about the space of string theory vacua (``the landscape'') to find statistical grounds to justify how and why the theory selects its vacuum. Particularly interesting are those vacua that preserve some supersymmetry, which are always supersymmetric solutions of some supergravity theory. After an general introduction to how the pursuit of unification has lead to the vacuum selection problem, we are going to review some recent results on the problem of finding all the supersymmetric solutions of a supergravity theory applied to the N=4,d=4 supergravity case.

gr-qc↗
arXiv2005

All the supersymmetric configurations of N=4,d=4 supergravity

All the supersymmetric configurations of pure, ungauged, N=4,d=4 supergravity are classified in a formalism that keeps manifest the S and T dualities of the theory. We also find simple equations that need to be satisfied by the configurations to be classical solutions of the theory. While the solutions associated to null Killing vectors were essentially classified by Tod (a classification that we refine), we find new configurations and solutions associated to timelike Killing vectors that do not satisfy Tod's rigidity hypothesis (hence, they have a non-trivial U(1) connection) and whose supersymmetry projector is associated to 1-dimensional objects (strings), although they have a trivial axion field.

hep-th↗
arXiv2005

A note on simple applications of the Killing Spinor Identities

We show how the Killing Spinor Identities (KSI) can be used to reduce the number of independent equations of motion that need to be checked explicitly to make sure that a supersymmetric configuration is a classical supergravity solution. We also show how the KSI can be used to compute BPS relations between masses and charges.

hep-th↗
arXiv2004

Agujeros negros clasicos y cuanticos en teoria de cuerdas

Introductory lectures on classical and quantum string black holes (supergravity, branes and dualities) given at the VII School "La Hechicera" of Relativity, Fields and Astrophysics, held in the University of Los Andes, Merida (Venezuela) 2001. Fully in Spanish.

hep-th↗
arXiv2004

Godel Spacetimes, Abelian Instantons, the Graviphoton Background and other Flacuum Solutions

We study the relations between all the vacua of Lorentzian and Euclidean d=4,5,6 SUGRAs with 8 supercharges, finding a new limiting procedure that takes us from the over-rotating near-horizon BMPV black hole to the Godel spacetime. The timelike compactification of the maximally supersymmetric Godel solution of N=1,d=5 SUGRA gives a maximally supersymmetric solution of pure Euclidean N=2,d=4 with flat space but non-trivial anti-selfdual vector field flux (``flacuum'') that, on the one hand, can be interpreted as an U(1) instanton on the 4-torus and that, on the other hand, coincides with the graviphoton background shown by Berkovits and Seiberg to produce the C-deformation introduced recently by Ooguri and Vafa. We construct flacuum solutions in other theories such as Euclidean type IIA supergravity.

hep-th↗
arXiv2003

The Bianchi Classification of Maximal D=8 Gauged Supergravities

We perform the generalised dimensional reduction of D=11 supergravity over three-dimensional group manifolds as classified by Bianchi. Thus, we construct eleven different maximal D=8 gauged supergravities, two of which have an additional parameter. One class of group manifolds (class B) leads to supergravities that are defined by a set of equations of motion that cannot be integrated to an action. All 1/2 BPS domain wall solutions are given. We also find a non-supersymmetric domain wall solution where the single transverse direction is time. This solution describes an expanding universe and upon reduction gives the Einstein-de Sitter universe in D=4. The uplifting of the different solutions to M-theory and the isometries of the corresponding group manifold are discussed.

hep-th↗
arXiv2002

On d=4,5,6 Vacua with 8 Supercharges

We show how all known N=2, d=4,5,6 maximally supersymmetric vacua (Hpp-waves and aDSxS solutions) are related through dimensional reduction/oxidation preserving all the unbroken supersymmetries. In particular we show how the N=2, d=5 family of vacua (which are the near-horizon geometry of supersymmetric rotating black holes) interpolates between aDS_2xS^3 and aDS_3xS^2 in parameter space and how it can be dimensionally reduced to an N=2, d=4 dyonic Robinson-Bertotti solution with geometry aDS_2xS^2 and oxidized to an N=2, d=6 solution with aDS_3xS^3 geometry (which is the near-horizon of the self-dual string).

hep-th↗
arXiv2002

Supergravity Vacua Today

We review the definition of (maximally supersymmetric) vacuum in supergravity theories, the currently known vacua in arbitrary dimensions and how the associated supersymmetry algebras can be found. (Invited talk at the Spanish Relativity Meeting (``EREs'') 2002, Mao, Menorca, September 21-23 2002.)

gr-qc↗
arXiv2002

Gauged/Massive Supergravities in Diverse Dimensions

We show how massive/gauged maximal supergravities in 11-n dimensions with SO(n-l,l) gauge groups (and other non-semisimple subgroups of Sl(n,R)) can be systematically obtained by dimensional reduction of ``massive 11-dimensional supergravity''. This series of massive/gauged supergravities includes, for instance, Romans' massive N=2A,d=10 supergravity for n=1, N=2,d=9 SO(2) and SO(1,1) gauged supergravities for n=2, and N=8,d=5 SO(6-l,l) gauged supergravity. In all cases, higher p-form fields get masses through the Stuckelberg mechanism which is an alternative to self-duality in odd dimensions.

hep-th↗
arXiv2002

A Note on Lie-Lorentz Derivatives

The definition of ``Lie derivative'' of spinors with respect to Killing vectors is extended to all kinds of Lorentz tensors. This Lie-Lorentz derivative appears naturally in the commutator of two supersymmetry transformations generated by Killing spinors and vanishes for Vielbeins. It can be identified as the generator of the action of isometries on supergravity fields and its use for the calculation of supersymmetry algebras is revised and extended.

hep-th↗
arXiv2001

Type 0 T-Duality and the Tachyon Coupling

We consider the T-duality relations between Type 0A and 0B theories, and show that this constraints the possible couplings of the tachyon to the RR-fields. Due to the `doubling' of the RR sector in Type 0 theories, we are able to introduce a democratic formulation for the Type 0 effective actions, in which there is no Chern-Simons term in the effective action. Finally we discuss how to embed Type II solutions into Type 0 theories.

hep-th↗
arXiv2000

7-Branes and Higher Kaluza-Klein Branes

We present and study a new chain of 10-d T duality related solutions and their 11-d parents whose existence had been predicted in the literature based in U duality requirements in 4 d. The first link is the S dual of the D7-brane. The next link has 6 spatial worldvolume dimensions, it is charged w.r.t. the RR 7-form but depends only on 2 transverse dimensions since the third has to be compactified in a circle and is isometric and hence is similar in this respect to the KK monopole. The next link has 5 spatial worldvolume dimensions, it is charged w.r.t. the RR 6-form but depends only on 2 transverse dimensions since the 3rd and 4th have to be compactified in circles and are isometric and so on. All these solutions are identical when reduced over the p spatial worldvolume dimensions and preserve a 1/2 on the supersymmetries. Their masses depend on the square of the radii of the isometric directions, just as for the KK monopole. We give a general map of these branes and their duality relations and show how they must appear in the supersymmetry algebra.

hep-th↗