511 research outputs found
Intersecting Branes, Defect Conformal Field Theories and Tensionless Strings
The defect conformal field theory describing intersecting D3-branes at a
C^2/Z_k orbifold is used to (de)construct the theory of intersecting M5-branes,
as well as M5-branes wrapping the holomorphic curve xy=c. The possibility of a
't Hooft anomaly due to tensionless strings at the intersection is discussed.
This note is based on a talk given by Zachary Guralnik at the 35th
International Symposium Ahrenshoop on the Theory of Elementary Particles.Comment: latex, one figure, 9pages. Talk given by Z.G. at the 35th
International Symposium Ahrenshoop on the Theory of Elementary Particle
Fluid dynamics of R-charged black holes
We construct electrically charged AdS_5 black hole solutions whose charge,
mass and boost-parameters vary slowly with the space-time coordinates. From the
perspective of the dual theory, these are equivalent to hydrodynamic
configurations with varying chemical potential, temperature and velocity
fields. We compute the boundary theory transport coefficients associated with a
derivative expansion of the energy momentum tensor and R-charge current up to
second order. In particular, we find a first order transport coefficient
associated with the axial component of the current.Comment: 31 pages, v2: published version; added some references, discussion of
the charge-current changed, results unchanged, v3: typo in formula (15)
changed, v4: added footnote 3 in order to clarify the relation of our results
to those of arXiv:0809.259
Towards quantifying information flows: Relative entropy in deep neural networks and the renormalization group
We investigate the analogy between the renormalization group (RG) and deep neural networks, wherein subsequent layers of neurons are analogous to successive steps along the RG. In particular, we quantify the flow of information by explicitly computing the relative entropy or Kullback-Leibler divergence in both the one- and two-dimensional Ising models under decimation RG, as well as in a feedforward neural network as a function of depth. We observe qualitatively identical behavior characterized by the monotonic increase to a parameter-dependent asymptotic value. On the quantum field theory side, the monotonic increase confirms the connection between the relative entropy and the c-theorem. For the neural networks, the asymptotic behavior may have implications for various information maximization methods in machine learning, as well as for disentangling compactness and generalizability. Furthermore, while both the two-dimensional Ising model and the random neural networks we consider exhibit non-trivial critical points, the relative entropy appears insensitive to the phase structure of either system. In this sense, more refined probes are required in order to fully elucidate the flow of information in these models. (C) Copyright J. Erdmenger et al. This work is licensed under the Creative Commons Attribution 4.0 International License. Published by the SciPost Foundation
Gauge/Gravity Duality and Some Applications
We discuss the AdS/CFT correspondence in which space-time emerges from an
interacting theory of D-branes and open strings. These ideas have a historical
continuity with QCD which is an interacting theory of quarks and gluons. In
particular we review the classic case of D3 branes and the non-conformal D1
brane system. We outline by some illustrative examples the calculations that
are enabled in a strongly coupled gauge theory by correspondence with dynamical
horizons in semi-classical gravity in one higher dimension. We also discuss
implications of the gauge-fluid/gravity correspondence for the information
paradox of black hole physics.Comment: 19 pages, 2 figures, Contribution to "Conference in Honor of Murray
Gell-Mann's 80th Birthday
Low-Energy Theorems from Holography
In the context of gauge/gravity duality, we verify two types of gauge theory
low-energy theorems, the dilation Ward identities and the decoupling of heavy
flavor. First, we provide an analytic proof of non-trivial dilation Ward
identities for a theory holographically dual to a background with gluon
condensate (the self-dual Liu--Tseytlin background). In this way an important
class of low-energy theorems for correlators of different operators with the
trace of the energy-momentum tensor is established, which so far has been
studied in field theory only. Another low-energy relationship, the so-called
decoupling theorem, is numerically shown to hold universally in three
holographic models involving both the quark and the gluon condensate. We show
this by comparing the ratio of the quark and gluon condensates in three
different examples of gravity backgrounds with non-trivial dilaton flow. As a
by-product of our study, we also obtain gauge field condensate contributions to
meson transport coefficients.Comment: 32 pages, 4 figures, two references added, typos remove
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
Criticality, Scaling and Chiral Symmetry Breaking in External Magnetic Field
We consider a D7-brane probe of in the presence of pure
gauge -field. The dual gauge theory is flavored Yang-Mills theory in
external magnetic field. We explore the dependence of the fermionic condensate
on the bare quark mass and study the discrete self-similar behavior of
the theory near the origin of the parametric space. We calculate the critical
exponents of the bare quark mass and the fermionic condensate. A study of the
meson spectrum supports the expectation based on thermodynamic considerations
that at zero bare quark mass the stable phase of the theory is a chiral
symmetry breaking one. Our study reveals the self-similar structure of the
spectrum near the critical phase of the theory, characterized by zero fermionic
condensate and we calculate the corresponding critical exponent of the meson
spectrum.Comment: 29 pages, 9 figures. Accepted in JHEP. Updated to mach the published
version. One figure added, some definitions improve
Properties of Chiral Wilson Loops
We study a class of Wilson Loops in N =4, D=4 Yang-Mills theory belonging to
the chiral ring of a N=2, d=1 subalgebra. We show that the expectation value of
these loops is independent of their shape. Using properties of the chiral ring,
we also show that the expectation value is identically 1. We find the same
result for chiral loops in maximally supersymmetric Yang-Mills theory in three,
five and six dimensions. In seven dimensions, a generalized Konishi anomaly
gives an equation for chiral loops which closely resembles the loop equations
of the three dimensional Chern-Simons theory.Comment: 15 pages, two pictures, some references adde
Adding flavour to the Polchinski-Strassler background
As an extension of holography with flavour, we analyze in detail the
embedding of a D7-brane probe into the Polchinski-Strassler gravity background,
in which the breaking of conformal symmetry is induced by a 3-form flux G_3.
This corresponds to giving masses to the adjoint chiral multiplets. We consider
the N=2 supersymmetric case in which one of the adjoint chiral multiplets is
kept massless while the masses of the other two are equal. This setup requires
a generalization of the known expressions for the backreaction of G_3 in the
case of three equal masses to generic mass values. We work to second order in
the masses to obtain the embedding of D7-brane probes in the background. At
this order, the 2-form potentials corresponding to the background flux induce
an 8-form potential which couples to the worldvolume of the D7-branes. We show
that the embeddings preserve an SU(2) x SU(2) symmetry. We study possible
embeddings both analytically in a particular approximation, as well as
numerically. The embeddings preserve supersymmetry, as we investigate using the
approach of holographic renormalization. The meson spectrum associated to one
of the embeddings found reflects the presence of the adjoint masses by
displaying a mass gap.Comment: LaTeX, 50 pages, 9 figure
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