609 research outputs found
Vacuum thin shell solutions in five-dimensional Lovelock gravity
Junction conditions for vacuum solutions in five-dimensional
Einstein-Gauss-Bonnet gravity are studied. We focus on those cases where two
spherically symmetric regions of space-time are joined in such a way that the
induced stress tensor on the junction surface vanishes. So a spherical vacuum
shell, containing no matter, arises as a boundary between two regions of the
space-time. Such solutions are a generalized kind of spherically symmetric
empty space solutions, described by metric functions of the class . New
global structures arise with surprising features. In particular, we show that
vacuum spherically symmetric wormholes do exist in this theory. These can be
regarded as gravitational solitons, which connect two asymptotically (Anti)
de-Sitter spaces with different masses and/or different effective cosmological
constants. We prove the existence of both static and dynamical solutions and
discuss their (in)stability under perturbations that preserve the symmetry.
This leads us to discuss a new type of instability that arises in
five-dimensional Lovelock theory of gravity for certain values of the coupling
of the Gauss-Bonnet term.Comment: 9 pages. This is an extended version of the authors' contribution to
the Proceedings of the Marcel Grossmann Meeting, held in Paris, 12-18 July
200
The Stoyanovsky-Ribault-Teschner Map and String Scattering Amplitudes
Recently, Ribault and Teschner pointed out the existence of a one-to-one
correspondence between N-point correlation functions for the SL(2,C)_k/SU(2)
WZNW model on the sphere and certain set of 2N-2-point correlation functions in
Liouville field theory. This result is based on a seminal work by Stoyanovsky.
Here, we discuss the implications of this correspondence focusing on its
application to string theory on curved backgrounds. For instance, we analyze
how the divergences corresponding to worldsheet instantons in AdS_3 can be
understood as arising from the insertion of the dual screening operator in the
Liouville theory side. We also study the pole structure of N-point functions in
the 2D Euclidean black hole and its holographic meaning in terms of the Little
String Theory. This enables us to interpret the correspondence between CFTs as
encoding a LSZ-type reduction procedure. Furthermore, we discuss the scattering
amplitudes violating the winding number conservation in those backgrounds and
provide a formula connecting such amplitudes with observables in Liouville
field theory. Finally, we study the WZNW correlation functions in the limit k
-> 0 and show that, at the point k=0, the Stoyanovsky-Ribault-Teschner
dictionary turns out to be in agreement with the FZZ conjecture at a particular
point of the space of parameters where the Liouville central charge becomes
c=-2. This result makes contact with recent studies on the dynamical tachyon
condensation in closed string theory.Comment: 30 pages; no figure
Energy in higher-derivative gravity via topological regularization
Indexación: Scopus.We give a novel definition of gravitational energy for an arbitrary theory of gravity including quadratic-curvature corrections to Einstein's equations. We focus on the theory in four dimensions, in the presence of a negative cosmological constant, and with asymptotically anti-de Sitter (AdS) boundary conditions. As a first example, we compute the gravitational energy and angular momentum of Schwarzschild-AdS black holes, for which we obtain results consistent with previous computations performed using different methods. However, our method is qualitatively different due to the fact that it is intrinsically nonlinear. It relies on the idea of adding to the gravity action topological invariant terms which suffice to regularize the Noether charges and render the variational problem well-posed. This is an idea that has been previously considered in the case of second-order theories, such as general relativity and which, as shown here, extends to higher-derivative theories. Besides black holes, we consider other solutions such as gravitational waves in AdS, for which we also find results that are in agreement. This enables us to investigate the consistency of this approach in the non-Einstein sector of the theory. © 2018 authors. Published by the American Physical Society.https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.04404
Superstrings on AdS3 at k=1
We study superstring theory in three dimensional Anti-de Sitter spacetime
with NS-NS flux, focusing on the case where the radius of curvature is equal to
the string length. This corresponds to the critical level k=1 in the
Wess-Zumino-Witten description. Previously, it was argued that a transition
takes place at this special radius, from a phase dominated by black holes at
larger radius to one dominated by long strings at smaller radius. We argue that
the infinite tower of modes that become massless at k=1 is a signal of this
transition. We propose a simple two-dimensional conformal field theory as the
holographic dual to superstring theory at k=1. As evidence for our conjecture,
we demonstrate that at large N our putative dual exactly reproduces the full
spectrum of the long strings of the weakly coupled string theory, including
states unprotected by supersymmetry.Comment: 29 pages, one figure. An equivalent construction of the dual orbifold
CFT has been added, together with a discussion of the short string spectrum
and additional observations on interaction
Spectral Flow in AdS(3)/CFT(2)
We study the spectral flowed sectors of the H3 WZW model in the context of
the holographic duality between type IIB string theory in AdS(3)x S^3 x T^4
with NSNS flux and the symmetric product orbifold of T^4. We construct
explicitly the physical vertex operators in the flowed sectors that belong to
short representations of the superalgebra, thus completing the bulk-to-boundary
dictionary for 1/2 BPS states. We perform a partial calculation of the string
three-point functions of these operators. A complete calculation would require
the three-point couplings of non-extremal flowed operators in the H3 WZW model,
which are at present unavailable. In the unflowed sector, perfect agreement has
recently been found between the bulk and boundary three-point functions of 1/2
BPS operators. Assuming that this agreement persists in the flowed sectors, we
determine certain unknown three-point couplings in the H3 WZW model in terms of
three-point couplings of affine descendants in the SU(2) WZW model.Comment: 50 pages, 2 figure
On AGT description of N=2 SCFT with N_f=4
We consider Alday-Gaiotto-Tachikawa (AGT) realization of the Nekrasov
partition function of N=2 SCFT. We focus our attention on the SU(2) theory with
N_f=4 flavor symmetry, whose partition function, according to AGT, is given by
the Liouville four-point function on the sphere. The gauge theory with N_f=4 is
known to exhibit SO(8) symmetry. We explain how the Weyl symmetry
transformations of SO(8) flavor symmetry are realized in the Liouville theory
picture. This is associated to functional properties of the Liouville
four-point function that are a priori unexpected. In turn, this can be thought
of as a non-trivial consistency check of AGT conjecture. We also make some
comments on elementary surface operators and WZW theory.Comment: 18 pages. v2, a misinterpretation in the gauge theory side has been
corrected; title and introduction were changed accordingl
Komar Integrals in Higher (and Lower) Derivative Gravity
The Komar integral relation of Einstein gravity is generalized to Lovelock
theories of gravity. This includes, in particular, a new boundary integral for
the Komar mass in Einstein gravity with a nonzero cosmological constant, which
has a finite result for asymptotically AdS black holes, without the need for an
infinite background subtraction. Explicit computations of the Komar mass are
given for black holes in pure Lovelock gravities of all orders and in general
Gauss-Bonnet theories.Comment: 16 pages; v2 - references and comment on relation to Noether charge
method adde
Conformal invariance and apparent universality of semiclassical gravity
In a recent work, it has been pointed out that certain observables of the
massless scalar field theory in a static spherically symmetric background
exhibit a universal behavior at large distances. More precisely, it was shown
that, unlike what happens in the case the coupling to the curvature \xi is
generic, for the special cases \xi=0 and \xi = 1/6 the large distance behavior
of the expectation value turns out to be independent of the
internal structure of the gravitational source. Here, we address a higher
dimensional generalization of this result: We first compute the difference
between a black hole and a static spherically symmetric star for the
observables and in the far field limit. Thus, we show
that the conformally invariant massless scalar field theory in a static
spherically symmetric background exhibits such universality phenomenon in D\geq
4 dimensions. Also, using the one-loop effective action, we compute
for a weakly gravitating object. These results lead to the
explicit expression of the expectation value for a
Schwarzschild-Tangherlini black hole in the far field limit. As an application,
we obtain quantum corrections to the gravitational potential in D dimensions,
which for D=4 are shown to agree with the one-loop correction to the graviton
propagator previously found in the literature.Comment: 11 page
Exploring Phylogenetic Relationships within Myriapoda and the Effects of Matrix Composition and Occupancy on Phylogenomic Reconstruction
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