44,164 research outputs found
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 model. As an
application, we explicitly provide W and the solutions to the related gradient
flows for the 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
U-Invariants, Black-Hole Entropy and Fixed Scalars
The absolute (moduli-independent) U-invariants of all N>2 extended
supergravities at D=4 are derived in terms of (moduli-dependent) central and
matter charges. These invariants give a general definition of the
``topological'' Bekenstein-Hawking entropy formula for extremal black-holes and
reduce to the square of the black-hole ADM mass for ``fixed scalars'' which
extremize the black-hole ``potential'' energy. The Hessian matrix of the
black-hole potential at ``fixed scalars'', in contrast to N=2 theories, is
shown to be degenerate, with rank (N-2)(N-3) + 2 n (N being the number of
supersymmetries and n the number of matter multiplets) and semipositive
definite.Comment: 11 pages, LaTeX, no figure
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)
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
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