439 research outputs found
General covariance, and supersymmetry without supersymmetry
An unusual four-dimensional generally covariant and supersymmetric SU(2)
gauge theory is described. The theory has propagating degrees of freedom, and
is invariant under a local (left-handed) chiral supersymmetry, which is half
the supersymmetry of supergravity. The Hamiltonian 3+1 decomposition of the
theory reveals the remarkable feature that the local supersymmetry is a
consequence of Yang-Mills symmetry, in a manner reminiscent of how general
coordinate invariance in Chern-Simons theory is a consequence of Yang-Mills
symmetry. It is possible to write down an infinite number of conserved
currents, which strongly suggests that the theory is classically integrable. A
possible scheme for non-perturbative quantization is outlined. This utilizes
ideas that have been developed and applied recently to the problem of
quantizing gravity.Comment: 17 pages, RevTeX, two minor errors correcte
A study of open strings ending on giant gravitons, spin chains and integrability
We systematically study the spectrum of open strings attached to half BPS
giant gravitons in the N=4 SYM AdS/CFT setup. We find that some null
trajectories along the giant graviton are actually null geodesics of AdS_5x
S^5, so that we can study the problem in a plane wave limit setup. We also find
the description of these states at weak 't Hooft coupling in the dual CFT. We
show how the dual description is given by an open spin chain with variable
number of sites. We analyze this system in detail and find numerical evidence
for integrability. We also discover an interesting instability of long open
strings in Ramond-Ramond backgrounds that is characterized by having a
continuum spectrum of the string, which is separated from the ground state by a
gap. This instability arises from accelerating the D-brane on which the strings
end via the Ramond-Ramond field. From the integrable spin chain point of view,
this instability prevents us from formulating the integrable structure in terms
of a Bethe Ansatz construction.Comment: 38 pages+appendices, 9 figures. Uses JHEP3. v2: added reference
BF Actions for the Husain-Kuchar Model
We show that the Husain-Kuchar model can be described in the framework of BF
theories. This is a first step towards its quantization by standard
perturbative QFT techniques or the spin-foam formalism introduced in the
space-time description of General Relativity and other diff-invariant theories.
The actions that we will consider are similar to the ones describing the
BF-Yang-Mills model and some mass generating mechanisms for gauge fields. We
will also discuss the role of diffeomorphisms in the new formulations that we
propose.Comment: 21 pages (in DIN A4 format), minor typos corrected; to appear in
Phys. Rev.
Gravitational Instantons and Moduli Spaces of Topological 2-form Gravity
A topological version of four-dimensional (Euclidean) Einstein gravity which
we propose regards anti-self-dual 2-forms and an anti-self-dual part of the
frame connections as fundamental fields. The theory describes the moduli spaces
of conformally self-dual Einstein manifolds for the non-zero cosmological
constant case and Einstein-Kahlerian manifold with the vanishing real first
Chern class for the zero cosmological constant. In the non-zero cosmological
constant case, we evaluate the index of the elliptic complex associated with
the moduli space and calculate the partition function. We also clarify the
moduli space and its dimension for the zero cosmological constant case which
are related to the Plebansky's heavenly equations.Comment: 36pages, LaTex, TIT/HEP-247/COSMO-4
Recycling universe
If the effective cosmological constant is non-zero, our observable universe
may enter a stage of exponential expansion. In such case, regions of it may
tunnel back to the false vacuum of an inflaton scalar field, and inflation with
a high expansion rate may resume in those regions. An ``ideal'' eternal
observer would then witness an infinite succession of cycles from false vacuum
to true, and back. Within each cycle, the entire history of a hot universe
would be replayed. If there were several minima of the inflaton potential, our
ideal observer would visit each one of these minima with a frequency which
depends on the shape of the potential. We generalize the formalism of
stochastic inflation to analyze the global structure of the universe when this
`recycling' process is taken into account.Comment: 43 pages, 10 figure
1/N Effects in Non-Relativistic Gauge-Gravity Duality
We argue that higher-curvature terms in the gravitational Lagrangian lead,
via non-relativistic gauge-gravity duality, to finite renormalization of the
dynamical exponent of the dual conformal field theory. Our argument includes a
proof of the non-renormalization of the Schrodinger and Lifshitz metrics beyond
rescalings of their parameters, directly generalizing the AdS case. We use this
effect to construct string-theory duals of non-relativistic critical systems
with non-integer dynamical exponents, then use these duals to predict the
viscosity/entropy ratios of these systems. The predicted values weakly violate
the KSS bound.Comment: 26 pages, late
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