94 research outputs found
Separability and Killing Tensors in Kerr-Taub-NUT-de Sitter Metrics in Higher Dimensions
A generalisation of the four-dimensional Kerr-de Sitter metrics to include a
NUT charge is well known, and is included within a class of metrics obtained by
Plebanski. In this paper, we study a related class of Kerr-Taub-NUT-de Sitter
metrics in arbitrary dimensions D \ge 6, which contain three non-trivial
continuous parameters, namely the mass, the NUT charge, and a (single) angular
momentum. We demonstrate the separability of the Hamilton-Jacobi and wave
equations, we construct a closely-related rank-2 Staeckel-Killing tensor, and
we show how the metrics can be written in a double Kerr-Schild form. Our
results encompass the case of the Kerr-de Sitter metrics in arbitrary
dimension, with all but one rotation parameter vanishing. Finally, we consider
the real Euclidean-signature continuations of the metrics, and show how in a
limit they give rise to certain recently-obtained complete non-singular compact
Einstein manifolds.Comment: Author added, title changed, references added, focus of paper changed
to Killing tensors and separability. Latex, 13 page
Spinor Fields and Symmetries of the Spacetime
In the background of a stationary black hole, the "conserved current" of a
particular spinor field always approaches the null Killing vector on the
horizon. What's more, when the black hole is asymptotically flat and when the
coordinate system is asymptotically static, then the same current also
approaches the time Killing vector at the spatial infinity. We test these
results against various black hole solutions and no exception is found. The
spinor field only needs to satisfy a very general and simple constraint.Comment: 19 page
General Metrics of G_2 Holonomy and Contraction Limits
We obtain first-order equations for G_2 holonomy of a wide class of metrics
with S^3\times S^3 principal orbits and SU(2)\times SU(2) isometry, using a
method recently introduced by Hitchin. The new construction extends previous
results, and encompasses all previously-obtained first-order systems for such
metrics. We also study various group contractions of the principal orbits,
focusing on cases where one of the S^3 factors is subjected to an Abelian,
Heisenberg or Euclidean-group contraction. In the Abelian contraction, we
recover some recently-constructed G_2 metrics with S^3\times T^3 principal
orbits. We obtain explicit solutions of these contracted equations in cases
where there is an additional U(1) isometry. We also demonstrate that the only
solutions of the full system with S^3\times T^3 principal orbits that are
complete and non-singular are either flat R^4 times T^3, or else the direct
product of Eguchi-Hanson and T^3, which is asymptotic to R^4/Z_2\times T^3.
These examples are in accord with a general discussion of isometric fibrations
by tori which, as we show, in general split off as direct products. We also
give some (incomplete) examples of fibrations of G_2 manifolds by associative
3-tori with either T^4 or K3 as base.Comment: Latex, 27 page
Horava-Witten Stability: eppur si muove
We construct exact time-dependent solutions of the supergravity equations of
motion in which two initially non-singular branes, one with positive and the
other with negative tension, move together and annihilate each other in an
all-enveloping spacetime singularity. Among our solutions are the Horava-Witten
solution of heterotic M-theory and a Randall-Sundrum I type solution, both of
which are supersymmetric, i.e. BPS, in the time-independent case. In the
absence of branes our solutions are of Kasner type, and the source of
instability may ascribed to a failure to stabilise some of the modulus fields
of the compactification. It also raises questions about the viability of models
based on some sorts of negative tension brane.Comment: Latex, 22 pages, extended discussion of the global spacetime
structure, and reference adde
Kahler Potential for M-theory on a G_2 Manifold
We compute the moduli Kahler potential for M-theory on a compact manifold of
G_2 holonomy in a large radius approximation. Our method relies on an explicit
G_2 structure with small torsion, its periods and the calculation of the
approximate volume of the manifold. As a verification of our result, some of
the components of the Kahler metric are computed directly by integration over
harmonic forms. We also discuss the modification of our result in the presence
of co-dimension four singularities and derive the gauge-kinetic functions for
the massless gauge fields that arise in this case.Comment: 31 pages, Latex. Altered discussion of truncation of field content,
some typos corrected and references added. Version to appear in Phys. Rev .
Charged rotating dilaton black branes in AdS universe
We present the metric for the -dimensional charged rotating dilaton
black branes with cylindrical or toroidal horizons in the background of anti-de
Sitter spacetime. We find the suitable counterterm which removes the
divergences of the action in the presence of the dilaton potential in all
higher dimensions. We plot the Penrose diagrams of the spacetime and reveal
that the spacetime geometry crucially modifies in the presence of the dilaton
field. The conserved and thermodynamic quantities of the black branes are also
computed.Comment: 13 pages, 3 figures, to appear in Gen. Relat. Gravi
Slowly rotating charged black holes in anti-de Sitter third order Lovelock gravity
In this paper, we study slowly rotating black hole solutions in Lovelock
gravity (n=3). These exact slowly rotating black hole solutions are obtained in
uncharged and charged cases, respectively. Up to the linear order of the
rotating parameter a, the mass, Hawking temperature and entropy of the
uncharged black holes get no corrections from rotation. In charged case, we
compute magnetic dipole moment and gyromagnetic ratio of the black holes. It is
shown that the gyromagnetic ratio keeps invariant after introducing the
Gauss-Bonnet and third order Lovelock interactions.Comment: 14 pages, no figur
Tachyon Kinks on Unstable Dp-branes
In the context of tachyon effective theory coupled to Born-Infeld
electromagnetic fields, we obtain all possible singularity-free static flat
configurations of codimension one on unstable Dp-branes. Computed tension and
string charge density suggest that the obtained kinks are D(p-1) or
D(p-1)F1-branes.Comment: 22pages, LaTeX2e, 7figure
Higher Dimensional Charged Rotating Dilaton Black Holes
In this paper, we present the metric for the -dimensional charged slowly
rotating dilaton black hole with independent rotation
parameters, associated with orthogonal planes of rotation in the background
of asymptotically flat and asymptotically (anti)-de Sitter spacetime. The mass,
angular momentum and the gyromagnetic ratio of such a black hole are determined
for the arbitrary values of the dilaton coupling constant. We find that the
gyromagnetic ratio crucially depends on the dilaton coupling constant,
, and decreases with increasing in any dimension.Comment: 15 pages, 1 figur
Cardiomyocytes from human pluripotent stem cells: from laboratory curiosity to industrial biomedical platform
Cardiomyocytes from human pluripotent stem cells (hPSCs-CMs) could revolutionise biomedicine. Global burden of heart failure will soon reach USD $90bn, while unexpected cardiotoxicity underlies 28% of drug withdrawals. Advances in hPSC isolation, Cas9/CRISPR genome engineering and hPSC-CM differentiation have improved patient care, progressed drugs to clinic and opened a new era in safety pharmacology. Nevertheless, predictive cardiotoxicity using hPSC-CMs contrasts from failure to almost total success. Since this likely relates to cell immaturity, efforts are underway to use biochemical and biophysical cues to improve many of the ~ 30 structural and functional properties of hPSC-CMs towards those seen in adult CMs. Other developments needed for widespread hPSC-CM utility include subtype specification, cost reduction of large scale differentiation and elimination of the phenotyping bottleneck. This review will consider these factors in the evolution of hPSC-CM technologies, as well as their integration into high content industrial platforms that assess structure, mitochondrial function, electrophysiology, calcium transients and contractility. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel
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