12 research outputs found
Strong Coupling Phenomena on the Noncommutative Plane
We study strong coupling phenomena in U(1) gauge theory on the
non-commutative plane. To do so, we make use of a T-dual description in terms
of an limit of U(N) gauge theory on a commutative torus. The
magnetic flux on this torus is taken to be , while the area scales like
1/N, keeping fixed. With a few assumptions, we argue that the
speed of high frequency light in pure non-commutative QED is modified in the
non-commutative directions by the factor , where
is the non-commutative parameter. If charged flavours are included,
there is an upper bound on the momentum of a photon propagating in the
non-commutative directions, beyond which it is unstable against production of
charged pairs. We also discuss a particular limit of pure
non-commutative QED which is T-dual to a more conventional limit
with fixed. In the non-commutative description, this limit gives rise to
an exotic theory of open strings.Comment: 24 pages, latex, 2 figures, corrected typo in eqn 6.
Calibrated Surfaces and Supersymmetric Wilson Loops
We study the dual gravity description of supersymmetric Wilson loops whose
expectation value is unity. They are described by calibrated surfaces that end
on the boundary of anti de-Sitter space and are pseudo-holomorphic with respect
to an almost complex structure on an eight-dimensional slice of AdS_5 x S^5.
The regularized area of these surfaces vanishes, in agreement with field theory
non-renormalization theorems for the corresponding operators.Comment: 28 pages, 2 figure
Exact Statistics of Chaotic Dynamical Systems
We present an inverse method to construct large classes of chaotic invariant
sets together with their exact statistics. The associated dynamical systems are
characterized by a probability distribution and a two-form. While our emphasis
is on classical systems, we briefly speculate about possible applications to
quantum field theory, in the context of generalizations of stochastic
quantization.Comment: 18 pages, 5 figure
Spectral Flow on the Higgs Branch and AdS/CFT Duality
We use AdS/CFT duality to study the large N_c limit of the meson spectrum on
the Higgs branch of a strongly coupled, N=2 supersymmetric SU(N_c) gauge theory
with N_f =2 fundamental hypermultiplets. In the dual supergravity description,
the Higgs branch is described by SU(2) instanton configurations on D7-branes in
an AdS background. We compute the spectral flow parameterized by the size of a
single instanton. In the large N_c limit, there is a sense in which the flow
from zero to infinite instanton size, or Higgs VEV, can be viewed as a closed
loop. We show that this flow leads to a non-trivial rearrangement of the
spectrum.Comment: v2; 16 pages, 3 figures, LaTeX + JHEP class, 3 refs added, accepted
for publication by JHE
Anomalies without Massless Particles
Baryon and lepton number in the standard model are violated by anomalies,
even though the fermions are massive. This problem is studied in the context of
a two dimensional model. In a uniform background field, fermion production
arise from non-adiabatic behavior that compensates for the absence of massless
modes. On the other hand, for localized instanton-like configurations, there is
an adiabatic limit. In this case, the anomaly is produced by bound states which
travel across the mass gap. The sphaleron corresponds to a bound state at the
halfway point.Comment: (26 pages, 3 figures, uses harvmac and uufiles), UCSD/PTH 93-3
Dynamics of the chiral phase transition from AdS/CFT duality
We use Lorentzian signature AdS/CFT duality to study a first order phase
transition in strongly coupled gauge theories which is akin to the chiral phase
transition in QCD. We discuss the relation between the latent heat and the
energy (suitably defined) of the component of a D-brane which lies behind the
horizon at the critical temperature. A numerical simulation of a dynamical
phase transition in an expanding, cooling Quark-Gluon plasma produced in a
relativistic collision is carried out.Comment: 30 pages, 5 figure
Perturbative Instabilities on the Non-Commutative Torus, Morita Duality and Twisted Boundary Conditions
We study one-loop corrections in scalar and gauge field theories on the
non-commutative torus. For rational theta, Morita equivalence allows these
theories to be reformulated in terms of ordinary theories on a commutative
torus with twisted boundary conditions. UV/IR mixing does not lead to
singularities, however there can be large corrections. In particular, gauge
theories show tachyonic instabilities for some of the modes. We discuss their
relevance to spontaneous Z_N x Z_N symmetry breaking in the Morita dual SU(N)
theory due to electric flux condensation.Comment: 30 page
A World-Volume Perspective on the Recombination of Intersecting Branes
We study brane recombination for supersymmetric configurations of
intersecting branes in terms of the world-volume field theory. This field
theory contains an impurity, corresponding to the degrees of freedom localized
at the intersection. The Higgs branch, on which the impurity fields condense,
consists of vacua for which the intersection is deformed into a smooth
calibrated manifold. We show this explicitly using a superspace formalism for
which the calibration equations arise naturally from F- and D-flatness.Comment: References adde
(De)constructing Intersecting M5-branes
We describe intersecting M5-branes, as well as M5-branes wrapping the
holomorphic curve xy=c, in terms of a limit of a defect conformal field theory
with two-dimensional (4,0) supersymmetry. This dCFT describes the low-energy
theory of intersecting D3-branes at a C^2/Z_k orbifold. In an appropriate k ->
infinity limit, two compact spatial directions are generated. By identifying
moduli of the M5-M5 intersection in terms of those of the dCFT, we argue that
the SU(2)_L R-symmetry of the (4,0) defect CFT matches the SU(2) R-symmetry of
the N =2, d=4 theory of the M5-M5 intersection. We find a 't Hooft anomaly in
the SU(2)_L R-symmetry, suggesting that tensionless strings give rise to an
anomaly in the SU(2) R-symmetry of intersecting M5-branes.Comment: latex, 25 pages, 4 figure
Four-Dimensional Superconformal Theories with Interacting Boundaries or Defects
We study four-dimensional superconformal field theories coupled to
three-dimensional superconformal boundary or defect degrees of freedom.
Starting with bulk N=2, d=4 theories, we construct abelian models preserving
N=2, d=3 supersymmetry and the conformal symmetries under which the
boundary/defect is invariant. We write the action, including the bulk terms, in
N=2, d=3 superspace. Moreover we derive Callan-Symanzik equations for these
models using their superconformal transformation properties and show that the
beta functions vanish to all orders in perturbation theory, such that the
models remain superconformal upon quantization. Furthermore we study a model
with N=4 SU(N) Yang-Mills theory in the bulk coupled to a N=4, d=3
hypermultiplet on a defect. This model was constructed by DeWolfe, Freedman and
Ooguri, and conjectured to be conformal based on its relation to an AdS
configuration studied by Karch and Randall. We write this model in N=2, d=3
superspace, which has the distinct advantage that non-renormalization theorems
become transparent. Using N=4, d=3 supersymmetry, we argue that the model is
conformal.Comment: 30 pages, 4 figures, AMSLaTeX, revised comments on Chern-Simons term,
references adde