16 research outputs found
Asymptotic generators of fermionic charges and boundary conditions preserving supersymmetry
We use a covariant phase space formalism to give a general prescription for
defining Hamiltonian generators of bosonic and fermionic symmetries in
diffeomorphism invariant theories, such as supergravities. A simple and general
criterion is derived for a choice of boundary condition to lead to conserved
generators of the symmetries on the phase space. In particular, this provides a
criterion for the preservation of supersymmetries. For bosonic symmetries
corresponding to diffeomorphisms, our prescription coincides with the method of
Wald et al.
We then illustrate these methods in the case of certain supergravity theories
in . In minimal AdS supergravity, the boundary conditions such that the
supercharges exist as Hamiltonian generators of supersymmetry transformations
are unique within the usual framework in which the boundary metric is fixed. In
extended AdS supergravity, or more generally in the presence
of chiral matter superfields, we find that there exist many boundary conditions
preserving supersymmetry for which corresponding generators
exist. These choices are shown to correspond to a choice of certain arbitrary
boundary ``superpotentials,'' for suitably defined ``boundary superfields.'' We
also derive corresponding formulae for the conserved bosonic charges, such as
energy, in those theories, and we argue that energy is always positive, for any
supersymmetry-preserving boundary conditions. We finally comment on the
relevance and interpretation of our results within the AdS-CFT correspondence.Comment: 45 pages, Latex, no figures, v2: extended discussion of positive
energy theorem and explicit form of fermionic generators, references adde
Towards a Non-Relativistic Holographic Superfluid
We explore the phase structure of a holographic toy model of superfluid
states in non-relativistic conformal field theories. At low background mass
density, we find a familiar second-order transition to a superfluid phase at
finite temperature. Increasing the chemical potential for the probe charge
density drives this transition strongly first order as the low-temperature
superfluid phase merges with a thermodynamically disfavored high-temperature
condensed phase. At high background mass density, the system reenters the
normal phase as the temperature is lowered further, hinting at a
zero-temperature quantum phase transition as the background density is varied.
Given the unusual thermodynamics of the background black hole, however, it
seems likely that the true ground state is another configuration altogether.Comment: 13+5 pages, late
Holographic models of de Sitter QFTs
We describe the dynamics of strongly coupled field theories in de Sitter
spacetime using the holographic gauge/gravity duality. The main motivation for
this is to explore the possibility of dynamical phase transitions during
cosmological evolution. Specifically, we study two classes of theories: (i)
conformal field theories on de Sitter in the static patch which are maintained
in equilibrium at temperatures that may differ from the de Sitter temperature
and (ii) confining gauge theories on de Sitter spacetime. In the former case we
show the such states make sense from the holographic viewpoint in that they
have regular bulk gravity solutions. In the latter situation we add to the
evidence for a confinement/deconfinement transition for a large N planar gauge
theory as the cosmological acceleration is increased past a critical value. For
the field theories we study, the critical acceleration corresponds to a de
Sitter temperature which is less than the Minkowski space deconfinement
transition temperature by a factor of the spacetime dimension.Comment: 35 pages, LaTeX, 4 figures, v2: refs adde
Large-density field theory, viscosity, and "" singularities from string duals
We analyze systems where an effective large-N expansion arises naturally in
gauge theories without a large number of colors: a sufficiently large charge
density alone can produce a perturbative string ('tHooft) expansion. One
example is simply the well-known NS5/F1 system dual to , here viewed as a 5+1 dimensional theory at finite density. This model is
completely stable, and we find that the existing string-theoretic solution of
this model yields two interesting results. First, it indicates that the shear
viscosity is not corrected by effects in this system. For flow
perpendicular to the F1 strings the viscosity to entropy ratio take the usual
value , but for flow parallel to the F1's it vanishes as at low
temperature. Secondly, it encodes singularities in correlation functions coming
from low-frequency modes at a finite value of the momentum along the
directions. This may provide a strong coupling analogue of finite density
condensed matter systems for which fermionic constituents of larger operators
contribute so-called "" singularities. In the NS5/F1 example, stretched
strings on the gravity side play the role of these composite operators. We
explore the analogue for our system of the Luttinger relation between charge
density and the volume bounded by these singular surfaces. This model provides
a clean example where the string-theoretic UV completion of the gravity dual to
a finite density field theory plays a significant and calculable role.Comment: 28 pages. v2: added reference
The Bekenstein Formula and String Theory (N-brane Theory)
A review of recent progress in string theory concerning the Bekenstein
formula for black hole entropy is given. Topics discussed include p-branes,
D-branes and supersymmetry; the correspondence principle; the D- and M-brane
approach to black hole entropy; the D-brane analogue of Hawking radiation, and
information loss; D-branes as probes of black holes; and the Matrix theory
approach to charged and neutral black holes. Some introductory material is
included.Comment: 53 pages, LaTeX. v3: Typos fixed, minor updates, references added,
brief Note Added on AdS/CF