629 research outputs found
The geometry of extended null supersymmetry in M-theory
For supersymmetric spacetimes in eleven dimensions admitting a null Killing
spinor, a set of explicit necessary and sufficient conditions for the existence
of any number of arbitrary additional Killing spinors is derived. The necessary
and sufficient conditions are comprised of algebraic relationships, linear in
the spinorial components, between the spinorial components and their first
derivatives, and the components of the spin connection and four-form. The
integrability conditions for the Killing spinor equation are also analysed in
detail, to determine which components of the field equations are implied by
arbitrary additional supersymmetries and the four-form Bianchi identity. This
provides a complete formalism for the systematic and exhaustive investigation
of all spacetimes with extended null supersymmetry in eleven dimensions. The
formalism is employed to show that the general bosonic solution of eleven
dimensional supergravity admitting a structure defined by four Killing
spinors is either locally the direct product of with a
seven-manifold of holonomy, or locally the Freund-Rubin direct product of
with a seven-manifold of weak holonomy. In addition, all
supersymmetric spacetimes admitting a
structure are classified.Comment: 36 pages, latex; v2, section classifying all spacetimes admitting a
structure included; v3, typos
corrected. Final version to appear in Phys.Rev.
Calibrated Entanglement Entropy
The Ryu-Takayanagi prescription reduces the problem of calculating
entanglement entropy in CFTs to the determination of minimal surfaces in a dual
anti-de Sitter geometry. For 3D gravity theories and BTZ black holes, we
identify the minimal surfaces as special Lagrangian cycles calibrated by the
real part of the holomorphic one-form of a spacelike hypersurface. We show that
(generalised) calibrations provide a unified way to determine holographic
entanglement entropy from minimal surfaces, which is applicable to warped
AdS geometries. We briefly discuss generalisations to higher dimensions.Comment: v1 22 pages, 1 figure; v2 appendix improved and moved into the body
to show the application of calibrations to find minimal surfaces in warped
AdS, matches published versio
Mapping the G-structures and supersymmetric vacua of five-dimensional N=4 supergravity
We classify the supersymmetric vacua of N=4, d=5 supergravity in terms of
G-structures. We identify three classes of solutions: with R^3, SU(2) and
generic SO(4) structure. Using the Killing spinor equations, we fully
characterize the first two classes and partially solve the latter. With the N=4
graviton multiplet decomposed in terms of N=2 multiplets: the graviton, vector
and gravitino multiplets, we obtain new supersymmetric solutions corresponding
to turning on fields in the gravitino multiplet. These vacua are described in
terms of an SO(5) vector sigma-model coupled with gravity, in three or four
dimensions. A new feature of these N=4 vacua, which is not seen from an N=2
point of view, is the possibility for preserving more exotic fractions of
supersymmetry. We give a few concrete examples of these new supersymmetric
(albeit singular) solutions. Additionally, we show how by truncating the N=4,
d=5 set of fields to minimal supergravity coupled with one vector multiplet we
recover the known two-charge solutions.Comment: 31 pages, late
M-Horizons
We solve the Killing spinor equations and determine the near horizon
geometries of M-theory that preserve at least one supersymmetry. The M-horizon
spatial sections are 9-dimensional manifolds with a Spin(7) structure
restricted by geometric constraints which we give explicitly. We also provide
an alternative characterization of the solutions of the Killing spinor
equation, utilizing the compactness of the horizon section and the field
equations, by proving a Lichnerowicz type of theorem which implies that the
zero modes of a Dirac operator coupled to 4-form fluxes are Killing spinors. We
use this, and the maximum principle, to solve the field equations of the theory
for some special cases and present some examples.Comment: 36 pages, latex. Reference added, minor typos correcte
Brane Solitons for G_2 Structures in Eleven-Dimensional Supergravity Re-Visited
We investigate the four-dimensional supergravity theory obtained from the
compactification of eleven-dimensional supergravity on a smooth manifold of G_2
holonomy. We give a new derivation for the Kaehler potential associated with
the scalar kinetic term of the N=1 four-dimensional theory. We then examine
some solutions of the four-dimensional theory which arise from wrapped
M-branes.Comment: 11 Pages, Latex, references adde
Pressure-Induced Rotational Symmetry Breaking in URuSi
Phase transitions and symmetry are intimately linked. Melting of ice, for
example, restores translation invariance. The mysterious hidden order (HO)
phase of URuSi has, despite relentless research efforts, kept its
symmetry breaking element intangible. Here we present a high-resolution x-ray
diffraction study of the URuSi crystal structure as a function of
hydrostatic pressure. Below a critical pressure threshold kbar,
no tetragonal lattice symmetry breaking is observed even below the HO
transition K. For , however, a pressure-induced rotational
symmetry breaking is identified with an onset temperatures K.
The emergence of an orthorhombic phase is found and discussed in terms of an
electronic nematic order that appears unrelated to the HO, but with possible
relevance for the pressure-induced antiferromagnetic (AF) phase. Existing
theories describe the HO and AF phases through an adiabatic continuity of a
complex order parameter. Since none of these theories predicts a
pressure-induced nematic order, our finding adds an additional symmetry
breaking element to this long-standing problem.Comment: 6 pages, 4 figures and supplemental material
Probing partially localized supergravity background of fundamental string ending on Dp-brane
We study the dynamics of the probe fundamental string in the field background
of the partially localized supergravity solution for the fundamental string
ending on Dp-brane. We separately analyze the probe dynamics for its motion
along the worldvolume direction and the transverse direction of the source
Dp-brane. We compare the dynamics of the probe along the Dp-brane worldvolume
direction to the BIon dynamics.Comment: 20 pages, LaTeX, revised version to appear in Phys. Rev.
A deformation of AdS_5 x S^5
We analyse a one parameter family of supersymmetric solutions of type IIB
supergravity that includes AdS_5 x S^5. For small values of the parameter the
solutions are causally well-behaved, but beyond a critical value closed
timelike curves (CTC's) appear. The solutions are holographically dual to N=4
supersymmetric Yang-Mills theory on a non-conformally flat background with
non-vanishing R-currents. We compute the holographic energy-momentum tensor for
the spacetime and show that it remains finite even when the CTC's appear. The
solutions, as well as the uplift of some recently discovered AdS_5 black hole
solutions, are shown to preserve precisely two supersymmetries.Comment: 16 pages, v2: typos corrected and references adde
Equal charge black holes and seven dimensional gauged supergravity
We present various supergravity black holes of different dimensions with some
U(1) charges set equal in a simple, common form. Black hole solutions of seven
dimensional U(1)^2 gauged supergravity with three independent angular momenta
and two equal U(1) charges are obtained. We investigate the thermodynamics and
the BPS limit of this solution, and find that there are rotating supersymmetric
black holes without naked closed timelike curves. There are also supersymmetric
topological soliton solutions without naked closed timelike curves that have a
smooth geometry.Comment: 24 pages; v2, v3: minor change
Bubbling AdS Black Holes
We explore the non-BPS analog of `AdS bubbles', which are regular spherically
symmetric 1/2 BPS geometries in type IIB supergravity. They have regular
horizons and can be thought of as bubbling generalizations of non-extremal AdS
black hole solutions in five-dimensional gauged supergravity. Due to the
appearance of the Heun equation even at the linearized level, various
approximation and numerical methods are needed in order to extract information
about this system. We study how the vacuum expectation value and mass of a
particular dimension two chiral primary operator depend on the temperature and
chemical potential of the thermal Yang-Mills theory. In addition, the mass of
the bubbling AdS black holes is computed. As is shown numerically, there are
also non-BPS solitonic bubbles which are completely regular and arise from
continuous deformations of BPS AdS bubbles.Comment: 37 pages, 2 figure
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