288 research outputs found
Manifest SO(N) invariance and S-matrices of three-dimensional N=2,4,8 SYM
An on-shell formalism for the computation of S-matrices of SYM theories in
three spacetime dimensions is presented. The framework is a generalization of
the spinor-helicity formalism in four dimensions. The formalism is applied to
establish the manifest SO(N) covariance of the on-shell superalgebra relevant
to N =2,4 and 8 SYM theories in d=3. The results are then used to argue for the
SO(N) invariance of the S-matrices of these theories: a claim which is proved
explicitly for the four-particle scattering amplitudes. Recursion relations
relating tree amplitudes of three-dimensional SYM theories are shown to follow
from their four-dimensional counterparts. The results for the four-particle
amplitudes are verified by tree-level perturbative computations and a unitarity
based construction of the integrand corresponding to the leading perturbative
correction is also presented for the N=8 theory. For N=8 SYM, the manifest
SO(8) symmetry is used to develop a map between the color-ordered amplitudes of
the SYM and superconformal Chern-Simons theories, providing a direct connection
between on-shell observables of D2 and M2-brane theories.Comment: 28 page
Acceleration-Induced Deconfinement Transitions in de Sitter Spacetime
In this note, we consider confining gauge theories in defined by
or compactification of higher-dimensional conformal field theories
with gravity duals. We investigate the behavior of these theories on de Sitter
spacetime as a function of the Hubble parameter. We find that in each case, the
de Sitter vacuum state of the field theory (defined by Euclidian continuation
from a sphere) undergoes a deconfinement transition as the Hubble parameter is
increased past a critical value. In each case, the corresponding critical de
Sitter temperature is smaller than the corresponding Minkowski-space
deconfinement temperature by a factor nearly equal to the dimension of the de
Sitter spacetime. The behavior is qualitatively and quantitatively similar to
that for confining theories defined by compactification of CFTs, studied
recently in arXiv:1007.3996.Comment: 25 pages, 7 figure
Intersecting D4-branes Model of Holographic QCD and Tachyon Condensation
We consider the intersecting D4-brane and anti-D4-brane model of holographic
QCD, motivated by the model that has recently been suggested by Van Raamsdonk
and Whyte. We analyze such D4-branes by the use of the action with a
bi-fundamental ``tachyon'' field, so that we find the classical solutions
describing the intersecting D4-branes and the U-shaped D4-branes. We show that
the ``tachyon'' field in the bulk theory provides a current quark mass and a
quark condensate to the dual gauge theory and that the lowest modes of mesons
obtain mass via tachyon condensation. Then evaluating the properties of a pion,
one can reproduce Gell-Mann-Oakes-Renner relation.Comment: 24 pages, 5 figures; v2: refs. added; v3: discussions on Chern-Simons
terms are adde
Semiclassical Analysis of M2-brane in AdS_4 x S^7 / Z_k
We start from the classical action describing a single M2-brane on AdS_4 x
S^7/ Z_k and consider semiclassical fluctuaitions around a static, 1/2 BPS
configuration whose shape is AdS_2 x S^1. The internal manifold S^7/ Z_k is
described as a U(1) fibration over CP^3 and the static configuration is wrapped
on the U(1) fiber. Then the configuration is reduced to an AdS_2 world-sheet of
type IIA string on AdS_4 x CP^3 through the Kaluza-Klein reduction on the S^1.
It is shown that the fluctuations form an infinite set of N=1 supermultiplets
on AdS_2, for k=1,2. The set is invariant under SO(8) which may be consistent
with N=8 supersymmetry on AdS_2. We discuss the behavior of the fluctuations
around the boundary of AdS_2 and its relation to deformations of Wilson loop
operator.Comment: 27 pages, v2: references added, v3: major revision including the
clarification of k=2 case, references added, version to appear in JHE
Renormalization group approach to matrix models via noncommutative space
We develop a new renormalization group approach to the large-N limit of
matrix models. It has been proposed that a procedure, in which a matrix model
of size (N-1) \times (N-1) is obtained by integrating out one row and column of
an N \times N matrix model, can be regarded as a renormalization group and that
its fixed point reveals critical behavior in the large-N limit. We instead
utilize the fuzzy sphere structure based on which we construct a new map
(renormalization group) from N \times N matrix model to that of rank N-1. Our
renormalization group has great advantage of being a nice analog of the
standard renormalization group in field theory. It is naturally endowed with
the concept of high/low energy, and consequently it is in a sense local and
admits derivative expansions in the space of matrices. In construction we also
find that our renormalization in general generates multi-trace operators, and
that nonplanar diagrams yield a nonlocal operation on a matrix, whose action is
to transport the matrix to the antipode on the sphere. Furthermore the
noncommutativity of the fuzzy sphere is renormalized in our formalism. We then
analyze our renormalization group equation, and Gaussian and nontrivial fixed
points are found. We further clarify how to read off scaling dimensions from
our renormalization group equation. Finally the critical exponent of the model
of two-dimensional gravity based on our formalism is examined.Comment: 1+42 pages, 4 figure
Comments on black holes I: The possibility of complementarity
We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who
argue against black hole complementarity based on the claim that an infalling
observer 'burns' as he approaches the horizon. We show that in fact
measurements made by an infalling observer outside the horizon are
statistically identical for the cases of vacuum at the horizon and radiation
emerging from a stretched horizon. This forces us to follow the dynamics all
the way to the horizon, where we need to know the details of Planck scale
physics. We note that in string theory the fuzzball structure of microstates
does not give any place to 'continue through' this Planck regime. AMPS argue
that interactions near the horizon preclude traditional complementarity. But
the conjecture of 'fuzzball complementarity' works in the opposite way: the
infalling quantum is absorbed by the fuzzball surface, and it is the resulting
dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde
Mitochondrial Oxidative Stress Alters a Pathway in Caenorhabditis elegans Strongly Resembling That of Bile Acid Biosynthesis and Secretion in Vertebrates
Mammalian bile acids (BAs) are oxidized metabolites of cholesterol whose amphiphilic properties serve in lipid and cholesterol uptake. BAs also act as hormone-like substances that regulate metabolism. The Caenorhabditis elegans clk-1 mutants sustain elevated mitochondrial oxidative stress and display a slow defecation phenotype that is sensitive to the level of dietary cholesterol. We found that: 1) The defecation phenotype of clk-1 mutants is suppressed by mutations in tat-2 identified in a previous unbiased screen for suppressors of clk-1. TAT-2 is homologous to ATP8B1, a flippase required for normal BA secretion in mammals. 2) The phenotype is suppressed by cholestyramine, a resin that binds BAs. 3) The phenotype is suppressed by the knock-down of C. elegans homologues of BA–biosynthetic enzymes. 4) The phenotype is enhanced by treatment with BAs. 5) Lipid extracts from C. elegans contain an activity that mimics the effect of BAs on clk-1, and the activity is more abundant in clk-1 extracts. 6) clk-1 and clk-1;tat-2 double mutants show altered cholesterol content. 7) The clk-1 phenotype is enhanced by high dietary cholesterol and this requires TAT-2. 8) Suppression of clk-1 by tat-2 is rescued by BAs, and this requires dietary cholesterol. 9) The clk-1 phenotype, including the level of activity in lipid extracts, is suppressed by antioxidants and enhanced by depletion of mitochondrial superoxide dismutases. These observations suggest that C. elegans synthesizes and secretes molecules with properties and functions resembling those of BAs. These molecules act in cholesterol uptake, and their level of synthesis is up-regulated by mitochondrial oxidative stress. Future investigations should reveal whether these molecules are in fact BAs, which would suggest the unexplored possibility that the elevated oxidative stress that characterizes the metabolic syndrome might participate in disease processes by affecting the regulation of metabolism by BAs
Vortices in (2+1)d Conformal Fluids
We study isolated, stationary, axially symmetric vortex solutions in
(2+1)-dimensional viscous conformal fluids. The equations describing them can
be brought to the form of three coupled first order ODEs for the radial and
rotational velocities and the temperature. They have a rich space of solutions
characterized by the radial energy and angular momentum fluxes. We do a
detailed study of the phases in the one-parameter family of solutions with no
energy flux. This parameter is the product of the asymptotic vorticity and
temperature. When it is large, the radial fluid velocity reaches the speed of
light at a finite inner radius. When it is below a critical value, the velocity
is everywhere bounded, but at the origin there is a discontinuity. We comment
on turbulence, potential gravity duals, non-viscous limits and non-relativistic
limits.Comment: 39 pages, 10 eps figures, v2: Minor changes, refs, preprint numbe
Wilsonian Approach to Fluid/Gravity Duality
The problem of gravitational fluctuations confined inside a finite cutoff at
radius outside the horizon in a general class of black hole geometries
is considered. Consistent boundary conditions at both the cutoff surface and
the horizon are found and the resulting modes analyzed. For general cutoff
the dispersion relation is shown at long wavelengths to be that of a
linearized Navier-Stokes fluid living on the cutoff surface. A cutoff-dependent
line-integral formula for the diffusion constant is derived. The
dependence on is interpreted as renormalization group (RG) flow in the
fluid. Taking the cutoff to infinity in an asymptotically AdS context, the
formula for reproduces as a special case well-known results derived
using AdS/CFT. Taking the cutoff to the horizon, the effective speed of sound
goes to infinity, the fluid becomes incompressible and the Navier-Stokes
dispersion relation becomes exact. The resulting universal formula for the
diffusion constant reproduces old results from the membrane
paradigm. Hence the old membrane paradigm results and new AdS/CFT results are
related by RG flow. RG flow-invariance of the viscosity to entropy ratio is shown to follow from the first law of thermodynamics together with
isentropy of radial evolution in classical gravity. The ratio is expected to
run when quantum gravitational corrections are included.Comment: 34 pages, harvmac, clarified boundary conditio
Shock waves in strongly coupled plasmas
Shock waves are supersonic disturbances propagating in a fluid and giving
rise to dissipation and drag. Weak shocks, i.e., those of small amplitude, can
be well described within the hydrodynamic approximation. On the other hand,
strong shocks are discontinuous within hydrodynamics and therefore probe the
microscopics of the theory. In this paper we consider the case of the strongly
coupled N=4 plasma whose microscopic description, applicable for scales smaller
than the inverse temperature, is given in terms of gravity in an asymptotically
space. In the gravity approximation, weak and strong shocks should be
described by smooth metrics with no discontinuities. For weak shocks we find
the dual metric in a derivative expansion and for strong shocks we use
linearized gravity to find the exponential tail that determines the width of
the shock. In particular we find that, when the velocity of the fluid relative
to the shock approaches the speed of light the penetration depth
scales as . We compare the results with second
order hydrodynamics and the Israel-Stewart approximation. Although they all
agree in the hydrodynamic regime of weak shocks, we show that there is not even
qualitative agreement for strong shocks. For the gravity side, the existence of
shock waves implies that there are disturbances of constant shape propagating
on the horizon of the dual black holes.Comment: 47 pages, 8 figures; v2:typos corrected, references adde
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