42 research outputs found
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.Comment: 11 page
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.Comment: 13 page
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.Comment: 19 page
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.Comment: 14 pages, LaTeX, one figure, typos correcte
Stationary solutions of N=2 supergravity
We discuss general bosonic stationary configurations of N=2, D=4 supergravity
coupled to vector multiplets. The requirement of unbroken supersymmetries
imposes constraints on the holomorphic symplectic section of the underlying
special K\"ahler manifold. The corresponding solutions of the field equations
are completely determined by a set of harmonic functions. As examples we
discuss rotating black holes, Taub-NUT and Eguchi-Hanson like instantons for
the STU model. In addition, we discuss, in the static limit, worldsheet
instanton corrections to the STU black hole solution, in the neighbourhood of a
vanishing 4-cycle of the Calabi-Yau manifold. Our procedure is quite general
and includes all known black hole solutions that can be embedded into N=2
supergravity.Comment: Latex, 28 pages, typos corrected, version to appear in NP
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 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.Comment: 62 pages v2: fewer typos, and a few improvements in the text kindly
suggested by a refere
HamiltonâJacobi counterterms for EinsteinâGaussâBonnet gravity
The on-shell gravitational action and the boundary stress tensor are essential ingredients in the study of black hole thermodynamics. We employ the HamiltonâJacobi method to calculate the boundary counterterms necessary to remove the divergences and allow the study of the thermodynamics of EinsteinâGaussâBonnet black holes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85396/1/cqg10_17_175014.pd
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).Comment: 24 pages, LaTeX2
Five Dimensional Minimal Supergravities and Four Dimensional Complex Geometries
We discuss the relation between solutions admitting Killing spinors of
minimal supergravities in five dimensions and four dimensional complex
geometries. In the ungauged case (vanishing cosmological constant \Lambda=0)
the solutions are determined in terms of a hyper-Kahler base space; in the
gauged case (\Lambda<0) the complex geometry is Kahler; in the de Sitter case
(\Lambda>0) the complex geometry is hyper-Kahler with torsion (HKT). In the
latter case some details of the derivation are given. The method for
constructing explicit solutions is discussed in each case.Comment: 8 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting 2008 in Salamanca, Spai
Holographic c-theorems and higher derivative gravity
In AdS/CFT, the holographic Weyl anomaly computation relates the a-anomaly
coefficient to the properties of the bulk action at the UV fixed point. This
universal behavior suggests the possibility of a holographic c-theorem for the
a-anomaly under flows to the IR. We prove such a c-theorem for higher curvature
Lovelock gravity, where the bulk equations of motion remain second order. We
also explore f(R) gravity as a toy model where higher derivatives cannot be
avoided. In this case, monoticity of the flow requires an additional condition
related to the higher derivative nature of the theory. This is in contrast to
the case of f(R) black hole entropy, where the second law follows from
application of the full Einstein equations and the null energy condition.Comment: 15 pages, revtex, references adde