2,176 research outputs found
Unstable Giants
We find giant graviton solutions in Frolov's three parameter generalization
of the Lunin-Maldacena background. The background we study has
and .
This class of backgrounds provide a non-superymmetric example of the gauge
theory/gravity correspondence that can be tested quantitatively, as recently
shown by Frolov, Roiban and Tseytlin. The giant graviton solutions we find have
a greater energy than the point gravitons, making them unstable states. Despite
this, we find striking quantitative agreement between the gauge theory and
gravity descriptions of open strings attached to the giant.Comment: 1+24 pages, 2 figures; v2: coupling to NSNS B field included, refs
added and typos corrected; v3 new results on stability of giants included,
presentation improved, refs added; v4 final version to appear in Phys. Rev.
On gravitational couplings in D-brane action
We compute the two closed string graviton - two open string scalar scattering
amplitude on the disc to show that there is no second-derivative curvature -
scalar coupling term R X^2 in the low-energy effective action of a D-brane in
curved space in type II superstring theory.Comment: 15 pages, 1 figure, LaTex JHEP style; v2: reference added, typos
corrected; v3: section 2 rewritten due to an error in gauge fixing, appendix
added, conclusions unchange
Fermionic microstates within Painlev\'e-Gullstrand black hole
We consider the quantum vacuum of fermionic field in the presence of a
black-hole background as a possible candidate for the stabilized black hole.
The stable vacuum state (as well as thermal equilibrium states with arbitrary
temperature) can exist if we use the Painlev\'e-Gullstrand description of the
black hole, and the superluminal dispersion of the particle spectrum at high
energy, which is introduced in the free-falling frame. Such choice is inspired
by the analogy between the quantum vacuum and the ground state of quantum
liquid, in which the event horizon for the low-energy fermionic quasiparticles
also can arise. The quantum vacuum is characterized by the Fermi surface, which
appears behind the event horizon. We do not consider the back reaction, and
thus there is no guarantee that the stable black hole exists. But if it does
exist, the Fermi surface behind the horizon would be the necessary attribute of
its vacuum state. We also consider exact discrete spectrum of fermions inside
the horizon which allows us to discuss the problem of fermion zero modes.Comment: LaTeX, 20 pages, 2 figure
Baryon Spectra and AdS/CFT Correspondence
We provide a detailed map between wrapped D3-branes in Anti-de Sitter (AdS)
backgrounds and dibaryon operators in the corresponding conformal field theory
(CFT). The effective five dimensional action governing the dynamics of AdS
space contains a gauge field that mediates interactions between
objects possessing R-charge. We show that the charge of these wrapped
D3-branes as measured by the gauge field matches the R-charge of the dibaryons
expected from field theory considerations. We are able, through a careful probe
brane calculation in an background, to understand the
exact relation between the mass of the wrapped D3-brane and the dimension of
the corresponding dibaryon. We also make some steps toward matching the
counting of dibaryon operators in the CFT with the ground states of a
supersymmetric quantum mechanical system whose target space is the moduli space
of D-branes. Finally, we discuss BPS excitations of the D3-brane and compare
them with higher dimension operators in the CFT.Comment: 24 pages, typos correcte
Trans-Planckian Physics and the Spectrum of Fluctuations in a Bouncing Universe
In this paper, we calculate the spectrum of scalar field fluctuations in a
bouncing, asymptotically flat Universe, and investigate the dependence of the
result on changes in the physics on length scales shorter than the Planck
length which are introduced via modifications of the dispersion relation. In
this model, there are no ambiguities concerning the choice of the initial
vacuum state. We study an example in which the final spectrum of fluctuations
depends sensitively on the modifications of the dispersion relation without
needing to invoke complex frequencies. Changes in the amplitude and in the
spectral index are possible, in addition to modulations of the spectrum. This
strengthens the conclusions of previous work in which the spectrum of
cosmological perturbations in expanding inflationary cosmologies was studied,
and it was found that, for dispersion relations for which the evolution is not
adiabatic, the spectrum changes from the standard prediction of
scale-invariance.Comment: 10 pages, 6 figures, RevTeX4. Analytical determination of the
spectrum, corrected some typos, conclusions unchange
Induced Gravity on RS Branes
It is shown that a localized four-dimensional Einstein term, induced by
quantum corrections, modifies significantly the law of gravity in a
Randall-Sundrum brane world. In particular, the short-distance behavior of
gravity changes from five- to four-dimensional, while, depending on the values
of parameters, there can be an intermediate range where gravity behaves as in
five dimensions. The spectrum of graviton fluctuations around the brane, their
relative importance for the gravitational force, and the relevance of their
emission in the bulk for the brane cosmology are analysed. Finally, constraints
on parameters are derived from energy loss in astrophysical and particle
physics processes.Comment: 20 pages, 1 figure, JHEP.cl
BPS Condensates, Matrix Models and Emergent String Theory
A prescription is given for computing anomalous dimensions of single trace
operators in SYM at strong coupling and large using a reduced model of
matrix quantum mechanics. The method involves treating some parts of the
operators as "BPS condensates" which, in certain limit, have a dual description
as null geodesics on the . In the gauge theory, the condensate is similar
to a representative of the chiral ring and it is described by a background of
commuting matrices. Excitations around these condensates correspond to
excitations around this background and take the form of "string bits" which are
dual to the "giant magnons" of Hofman and Maldacena. In fact, the matrix model
approach gives a {\it quantum} description of these string configurations and
explains why the infinite momentum limit suppresses the quantum effects. This
method allows, not only to derive part of the classical sigma model Hamiltonian
of the dual string (in the infinite momentum limit), but also its quantum
canonical structure. Therefore, it provides an alternative method of testing
the AdS/CFT correspondence without the need of integrability.Comment: 36 pages, 1 figure, 2 appendices, v2: references adde
Instability of non-supersymmetric smooth geometries
Recently certain non-supersymmetric solutions of type IIb supergravity were
constructed [hep-th/0504181], which are everywhere smooth, have no horizons and
are thought to describe certain non-BPS microstates of the D1-D5 system. We
demonstrate that these solutions are all classically unstable. The instability
is a generic feature of horizonless geometries with an ergoregion. We consider
the endpoint of this instability and argue that the solutions decay to
supersymmetric configurations. We also comment on the implications of the
ergoregion instability for Mathur's `fuzzball' proposal.Comment: v2: typos corrected, reference adde
"Holey Sheets" - Pfaffians and Subdeterminants as D-brane Operators in Large N Gauge Theories
In the AdS/CFT correspondence, wrapped D3-branes (such as "giant gravitons")
on the string theory side of the correspondence have been identified with
Pfaffian, determinant and subdeterminant operators on the field theory side. We
substantiate this identification by showing that the presence of pairs of such
operators in a correlation function of a large N gauge theory naturally leads
to a modified 't Hooft expansion including also worldsheets with boundaries.
This happens independently of supersymmetry or conformal invariance.Comment: 39 pages, 10 figures, harvma
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