10,460 research outputs found
Extremal Correlators in the AdS/CFT Correspondence
The non-renormalization of the 3-point functions of chiral primary operators in N=4 super-Yang-Mills theory is one of
the most striking facts to emerge from the AdS/CFT correspondence. A two-fold
puzzle appears in the extremal case, e.g. k_1 = k_2 + k_3. First, the
supergravity calculation involves analytic continuation in the k_i variables to
define the product of a vanishing bulk coupling and an infinite integral over
AdS. Second, extremal correlators are uniquely sensitive to mixing of the
single-trace operators with protected multi-trace operators in the
same representation of SU(4). We show that the calculation of extremal
correlators from supergravity is subject to the same subtlety of regularization
known for the 2-point functions, and we present a careful method which
justifies the analytic continuation and shows that supergravity fields couple
to single traces without admixture. We also study extremal n-point functions of
chiral primary operators, and argue that Type IIB supergravity requires that
their space-time form is a product of n-1 two-point functions (as in the free
field approximation) multiplied by a non-renormalized coefficient. This
non-renormalization property of extremal n-point functions is a new prediction
of the AdS/CFT correspondence. As a byproduct of this work we obtain the cubic
couplings and of fields in the dilaton and 5-sphere
graviton towers of Type IIB supergravity on .Comment: 26 pages, LateX, no figure
The Hidden Spatial Geometry of Non-Abelian Gauge Theories
The Gauss law constraint in the Hamiltonian form of the gauge theory
of gluons is satisfied by any functional of the gauge invariant tensor variable
. Arguments are given that the tensor is a more appropriate variable. When the Hamiltonian
is expressed in terms of or , the quantity appears.
The gauge field Bianchi and Ricci identities yield a set of partial
differential equations for in terms of . One can show that
is a metric-compatible connection for with torsion, and that the curvature
tensor of is that of an Einstein space. A curious 3-dimensional
spatial geometry thus underlies the gauge-invariant configuration space of the
theory, although the Hamiltonian is not invariant under spatial coordinate
transformations. Spatial derivative terms in the energy density are singular
when . These singularities are the analogue of the centrifugal
barrier of quantum mechanics, and physical wave-functionals are forced to
vanish in a certain manner near . It is argued that such barriers are
an inevitable result of the projection on the gauge-invariant subspace of the
Hilbert space, and that the barriers are a conspicuous way in which non-abelian
gauge theories differ from scalar field theories.Comment: 19 pages, TeX, CTP #223
Holographic RG-flows and Boundary CFTs
Solutions of -dimensional gravity coupled to a scalar field are
obtained, which holographically realize interface and boundary CFTs. The
solution utilizes a Janus-like slicing ansatz and corresponds
to a deformation of the CFT by a spatially-dependent coupling of a relevant
operator. The BCFT solutions are singular in the bulk, but physical quantities
such as the holographic entanglement entropy can be calculated.Comment: 26 pages, 11 figure
Heavy Quark Potentials in Some Renormalization Group Revised AdS/QCD Models
We construct some AdS/QCD models by the systematic procedure of GKN. These
models reflect three rather different asymptotics the gauge theory beta
functions approach at the infrared region,
and , where is the 't Hooft coupling constant.
We then calculate the heavy quark potentials in these models by holographic
methods and find that they can more consistently fit the lattice data relative
to the usual models which do not include the renormalization group improving
effects. But only use the lattice QCD heavy quark potentials as constrains, we
cannot distinguish which kind of infrared asymptotics is the better one.Comment: comparisons with lattice results, qualitative consideration of
quantum corrections are added. (accepted by Phys. Rev. D
On the massless contributions to the vacuum polarization of heavy quarks
Recently Groote and Pivovarov have given notice of a possible fault in the
use of sum rules involving two-point correlation functions to extract
information on heavy quark parameters, due to the presence of massless
contributions that invalidate the construction of moments of the spectral
densities. Here we show how to circumvent this problem through a new definition
of the moments, providing an infrared safe and consistent procedure.Comment: 1+9 pages, 3 figures. Discussion on QCD sum rules applications added.
Conclusions unchanged. Version to be published in Journal of Physics
From Soft Walls to Infrared Branes
Five dimensional warped spaces with soft walls are generalizations of the
standard Randall-Sundrum compactifications, where instead of an infrared brane
one has a curvature singularity (with vanishing warp factor) at finite proper
distance in the bulk. We project the physics near the singularity onto a
hypersurface located a small distance away from it in the bulk. This results in
a completely equivalent description of the soft wall in terms of an effective
infrared brane, hiding any singular point. We perform explicitly this
calculation for two classes of soft wall backgrounds used in the literature.
The procedure has several advantages. It separates in a clean way the physics
of the soft wall from the physics of the five dimensional bulk, facilitating a
more direct comparison with standard two-brane warped compactifications.
Moreover, consistent soft walls show a sort of universal behavior near the
singularity which is reflected in the effective brane Lagrangian. Thirdly, for
many purposes, a good approximation is obtained by assuming the bulk background
away from the singularity to be the usual Randall-Sundrum metric, thus making
the soft wall backgrounds better analytically tractable. We check the validity
of this procedure by calculating the spectrum of bulk fields and comparing it
to the exact result, finding very good agreement.Comment: 14 pages, 2 figures, v2: subsection on IR brane potentials and
appendix on fermions added, version to appear in PR
The Measure of Cosmological Parameters
New, large, ground and space telescopes are contributing to an exciting and
rapid period of growth in observational cosmology. The subject is now far from
its earlier days of being data-starved and unconstrained, and new data are
fueling a healthy interplay between observations and experiment and theory. I
briefly review here the status of measurements of a number of quantities of
interest in cosmology: the Hubble constant, the total mass-energy density, the
matter density, the cosmological constant or dark energy component, and the
total optical background light.Comment: 12 pages, 4 figures, to be published in "2001: A Spacetime Odyssey:
Proceedings of the Inaugural Conference of the Michigan Center for
Theoretical Physics", Michael J. Duff & James T. Liu, eds., (World
Scientific, Singapore), in pres
Holographic Dual of BCFT
We propose a holographic dual of a conformal field theory defined on a
manifold with boundaries, i.e. boundary conformal field theory (BCFT). Our new
holography, which may be called AdS/BCFT, successfully calculates the boundary
entropy or g-function in two dimensional BCFTs and it agrees with the finite
part of the holographic entanglement entropy. Moreover, we can naturally derive
a holographic g-theorem. We also analyze the holographic dual of an interval at
finite temperature and show that there is a first order phase transition.Comment: 5 pages, 3 figs, a reference added, typos corrected, to be published
in PR
Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain
We present a study of the local strain effects associated with vacancy
defects in strontium titanate and report the first calculations of elastic
dipole tensors and chemical strains for point defects in perovskites. The
combination of local and long-range results will enable determination of x-ray
scattering signatures that can be compared with experiments. We find that the
oxygen vacancy possesses a special property -- a highly anisotropic elastic
dipole tensor which almost vanishes upon averaging over all possible defect
orientations. Moreover, through direct comparison with experimental
measurements of chemical strain, we place constraints on the possible defects
present in oxygen-poor strontium titanate and introduce a conjecture regarding
the nature of the predominant defect in strontium-poor stoichiometries in
samples grown via pulsed laser deposition. Finally, during the review process,
we learned of recent experimental data, from strontium titanate films deposited
via molecular-beam epitaxy, that show good agreement with our calculated value
of the chemical strain associated with strontium vacancies.Comment: 14 pages, 11 figures, 4 table
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