Split Attractor Flow in N=2 Minimally Coupled Supergravity

We classify the stability region, marginal stability walls (MS) and split attractor flows for two-center extremal black holes in four-dimensional N=2 supergravity minimally coupled to n vector multiplets. It is found that two-center (continuous) charge orbits, classified by four duality invariants, either support a stability region ending on a MS wall or on an anti-marginal stability (AMS) wall, but not both. Therefore, the scalar manifold never contains both walls. Moreover, the BPS mass of the black hole composite (in its stability region) never vanishes in the scalar manifold. For these reasons, the "bound state transformation walls" phenomenon does not necessarily occur in these theories. The entropy of the flow trees also satisfies an inequality which forbids "entropy enigma" decays in these models. Finally, the non-BPS case, due to the existence of a "fake" superpotential satisfying a triangle inequality, can be treated as well, and it can be shown to exhibit a split attractor flow dynamics which, at least in the n=1 case, is analogous to the BPS one.Comment: 1+29 pages, 2 figures; v2: minor changes, especially in Sects. 1 and 2; Sect. 6 changed. To appear on NP

Black holes, first-order flow equations and geodesics on symmetric spaces

For both extremal and non-extremal spherically symmetric black holes in theories with massless scalars and vectors coupled to gravity, we derive a general form of first-order gradient flow equations, equivalent to the equations of motion. For theories that have a symmetric moduli space after a dimensional reduction over the timelike direction, we discuss the condition for such a gradient flow to exist. This note reviews the results of arXiv:0810.1528 [hep-th].Comment: 6 pages, contribution to the proceedings of the 4th RTN Workshop 'Constituents, Fundamental Forces and Symmetries of the Universe', Varna, 11-17 September 2008; v2: a reference adde

Universality of the superpotential for d = 4 extremal black holes

We provide a general strategy to obtain the superpotential W for both BPS and non-BPS extremal black holes in N=2 four dimensional supergravities based on symmetric spaces. This extends the construction of W in terms of U-duality invariants that was presented in previous work on the $t^3$ model. As an application, we explicitly provide W and the solutions to the related gradient flows for the $st^2$ and stu models. The procedure is shown to hold also for the full N=8 theory. The role of flat directions in moduli space is clarified.Comment: 29 pages. v2: typos corrected, comments and references adde

Orbits and Attractors for N=2 Maxwell-Einstein Supergravity Theories in Five Dimensions

BPS and non-BPS orbits for extremal black-holes in N=2 Maxwell-Einstein supergravity theories (MESGT) in five dimensions were classified long ago by the present authors for the case of symmetric scalar manifolds. Motivated by these results and some recent work on non-supersymmetric attractors we show that attractor equations in N=2 MESGTs in d=5 do indeed possess the distinct families of solutions with finite Bekenstein-Hawking entropy. The new non-BPS solutions have non-vanishing central charge and matter charge which is invariant under the maximal compact subgroup of the stabilizer of the non-BPS orbit. Our analysis covers all symmetric space theories G/H such that G is a symmetry of the action. These theories are in one-to-one correspondence with (Euclidean) Jordan algebras of degree three. In the particular case of N=2 MESGT with scalar manifold SU*(6)/USp(6) a duality of the two solutions with regard to N=2 and N=6 supergravity is also considered.Comment: Added a footnote on notation and comments on the attactor nature of non BPS solutions in section 5. Typos corrected. Version to appear in NPB. Latex file, 24 page

Spontaneous Breaking of Extended Supersymmetry in Global and Local Theories

We review the "no-go" theorems that severely constrain the breaking of N=2 supersymmetry to N=1 (both in rigid supersymmetry and supergravity), and we exhibit some models that evade them.Comment: Contribution to the proceedings of the Spring School and Workshop on String Theory, Gauge Theory and Quantum Gravity, ICTP, Trieste, Italy, March 18-29,1996. Latex file, uses espcrc2.sty and epsf.st

Perturbative and Non-perturbative N =8 Supergravity

We study extremal black holes, their ADM mass and area of the horizon in N = 8 supergravity. Contrary to intuition gained from N = 2, 4 theories, in N = 8 supergravity BPS states may become massless only at the boundary of moduli space. We show that stringy states described in [1], which have no mass gap and survive in the toroidal compactification in addition to massless states of perturbative N = 8 supergravity, display a null singularity in four-dimensional space-time, when viewed as solutions of N = 8 Einstein equations. We analyze known methods of resolving such singularities and explain why they do not work in D=4, N = 8 supergravity. We discuss possible implications for the issue of UV finiteness of the four-dimensional N = 8 perturbation theory.Comment: 5p, few corrections and improvements, references added, published in Physics Letter

Supergravity and the quest for a unified theory

A recollection of some theoretical developments that preceded and followed the first formulation of supergravity theory is presented. Special emphasis is placed on the impact of supergravity on the search for a unified theory of fundamental interactions.Comment: 15 pages, late

Web Services: A Process Algebra Approach

It is now well-admitted that formal methods are helpful for many issues raised in the Web service area. In this paper we present a framework for the design and verification of WSs using process algebras and their tools. We define a two-way mapping between abstract specifications written using these calculi and executable Web services written in BPEL4WS. Several choices are available: design and correct errors in BPEL4WS, using process algebra verification tools, or design and correct in process algebra and automatically obtaining the corresponding BPEL4WS code. The approaches can be combined. Process algebra are not useful only for temporal logic verification: we remark the use of simulation/bisimulation both for verification and for the hierarchical refinement design method. It is worth noting that our approach allows the use of any process algebra depending on the needs of the user at different levels (expressiveness, existence of reasoning tools, user expertise)