1,403 research outputs found
Gravitational duality, topologically massive gravity and holographic fluids
Self-duality in Euclidean gravitational set ups is a tool for finding
remarkable geometries in four dimensions. From a holographic perspective,
self-duality sets an algebraic relationship between two a priori independent
boundary data: the boundary energy-momentum tensor and the boundary Cotton
tensor. This relationship, which can be viewed as resulting from a topological
mass term for gravity boundary dynamics, survives under the Lorentzian
signature and provides a tool for generating exact bulk Einstein spaces
carrying, among others, nut charge. In turn, the holographic analysis exhibits
perfect-fluid-like equilibrium states and the presence of non-trivial vorticity
allows to show that infinite number of transport coefficients vanish.Comment: 37 page
String Theory on AdS3: Some Open Questions
String theory on curved backgrounds has received much attention on account of
both its own interest, and of its relation with gauge theories. Despite the
progress made in various directions, several quite elementary questions remain
unanswered, in particular in the very simple case of three-dimensional anti-de
Sitter space. I will very briefly review these problems, discuss in some detail
the important issue of constructing a consistent spectrum for a string
propagating on ADS3 plus torsion background, and comment on potential
solutions.Comment: 18 pages, latex. To appear in the proceedings of the TMR European
program meeting "Quantum aspects of gauge theories, supersymmetry and
unification", Paris, France, 1--7 September, 1999; v2: comments and
references adde
Corfu 05 lectures - part I: Strings on curved backgrounds
In these introductory lectures we summarize some basic facts and techniques
about perturbative string theory (sections 1 to 6). These are further developed
(sections 7 and 8) for describing string propagation in the presence of
gravitational or gauge fields. We also remind some solutions of the string
equations of motion, which correspond to remarkable (NS or D) brane
configurations.
A part II by Emilian Dudas will be devoted to orientifold constructions and
applications to string model building
Gravity, strings, modular and quasimodular forms
Modular and quasimodular forms have played an important role in gravity and
string theory. Eisenstein series have appeared systematically in the
determination of spectrums and partition functions, in the description of
non-perturbative effects, in higher-order corrections of scalar-field spaces,
... The latter often appear as gravitational instantons i.e. as special
solutions of Einstein's equations. In the present lecture notes we present a
class of such solutions in four dimensions, obtained by requiring (conformal)
self-duality and Bianchi IX homogeneity. In this case, a vast range of
configurations exist, which exhibit interesting modular properties. Examples of
other Einstein spaces, without Bianchi IX symmetry, but with similar features
are also given. Finally we discuss the emergence and the role of Eisenstein
series in the framework of field and string theory perturbative expansions, and
motivate the need for unravelling novel modular structures.Comment: 45 pages. To appear in the proceedings of the Besse Summer School on
Quasimodular Forms - 201
The influence of spectral truncation on the shape of short optical pulses
This paper studies the influence of spectral truncation on the shape of short optical pulses. As an application example, the case of third-order (m=3) transform-limited super-Gaussian pulses is considered through both simulations and experiments. This work can be used to optimize pulse shaping procedures in the frequency domain
Slowing of pulses to c/10 with subwatt power levels and low latency using Brillouin amplification in a bismuth-oxide optical fiber
We report the generation of slow light using Brillouin amplification in a short length of highly nonlinear bismuth-oxide fiber. By using just 2m of fiber, we demonstrate a five-fold reduction in group velocity for ~200ns pulses, which we believe to be a record for a slow-light propagation in an optical fiber. Moreover, by virtue of the high nonlinearity per unit length of this fiber, we achieve this at a very modest pump power level of just ~400mW and with a low inherent device latency of 14ns. These results highlight both the merits and practicality of using high nonlinearity nonsilica fibers for slow-light devices
Gravity duals of N=2 SCFTs and asymptotic emergence of the electrostatic description
We built the first eleven-dimensional supergravity solutions with
SO(2,4)xSO(3)xU(1)_R symmetry that exhibit the asymptotic emergence of an extra
U(1) isometry. This enables us to make the connection with the usual
electrostatics-quiver description. The solution is obtained via the Toda frame
of Kahler surfaces with vanishing scalar curvature and SU(2) action.Comment: 1+15 pages, Latex, v2: few minor changes, JHEP versio
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