115 research outputs found
Worldsheet four-point functions in AdS(3)/CFT(2)
We calculate some extremal and non-extremal four-point functions on the
sphere of certain chiral primary operators for strings on AdS_3 x S^3 x T^4.
The computation is done for small values of the spacetime cross-ratio where
global SL(2) and SU(2) descendants may be neglected in the intermediate
channel. Ignoring also current algebra descendants, we find that in the
non-extremal case the integrated worldsheet correlators factorize into
spacetime three-point functions, which is non-trivial due to the integration
over the moduli space. We then restrict to the extremal case and compare our
results with the four-point correlators recently computed in the dual boundary
theory. We also discuss a particular non-extremal correlator involving two
chiral and two anti-chiral operators.Comment: 34 pages, subsection on crossing symmetry adde
Chiral Primaries in Strange Metals
It was suggested recently that the study of 1-dimensional QCD with fermions
in the adjoint representation could lead to an interesting toy model for
strange metals and their holographic formulation. In the high density regime,
the infrared physics of this theory is described by a constrained free fermion
theory with an emergent {\cal N}=(2,2) superconformal symmetry. In order to
narrow the choice of potential holographic duals, we initiate a systematic
search for chiral primaries in this model. We argue that the bosonic part of
the superconformal algebra can be extended to a coset chiral algebra of the
form {\cal W}_N =\SO(2N^2-2)_1/\SU(N)_{2N}. In terms of this algebra the
spectrum of the low energy theory decomposes into a finite number of sectors
which are parametrized by special necklaces. We compute the corresponding
characters and partition functions and determine the set of chiral primaries
for N \leq 5.Comment: 42 pages, 5 figure
The D3/D7 Background and Flavor Dependence of Regge Trajectories
In the context of AdS/CFT with flavor, we consider the type IIB supergravity
solution corresponding to a fully localized D3/D7 intersection. We complete the
standard metric ansatz by providing an analytic expression for the warp factor,
under the assumption of a logarithmically running axion-dilaton. From the gauge
dual perspective, this behavior is related to the positive beta function of the
N=4, d=4 SU(N_c) super Yang-Mills gauge theory, coupled to N_f fundamental N=2
hypermultiplets. We comment on the existence of tadpoles and relate them to the
same gauge theory beta function. Next we consider a classical spinning string
configuration in the decoupling limit of the D3/D7 geometry and extract the
flavor (N_f) dependence of the associated meson Regge trajectory. Including the
backreaction of the D7-branes in the supergravity dual allows for going beyond
the quenched approximation on the dual gauge theory side.Comment: 26 pages, 5 figure
Chiral Ring of Strange Metals: The Multicolor Limit
The low energy limit of a dense 2D adjoint QCD is described by a family of
supersymmetric coset conformal field theories. In previous
work we constructed chiral primaries for a small number of colors. Our
aim in the present note is to determine the chiral ring in the multicolor limit
where is sent to infinity. We shall find that chiral primaries are labeled
by partitions and identify the ring they generate as the ring of Schur
polynomials. Our findings impose strong constraints on the possible dual
description through string theory in an compactification.Comment: 25 pages, 4 figure
Holographic heavy-light mesons from non-Abelian DBI
In the context of gauge/gravity duals with flavor, we examine heavy-light
mesons which involve a heavy and a light quark. For this purpose we embed two
D7 brane probes at different positions into the gravity background. We
establish the non-Abelian Dirac-Born-Infeld (DBI) action for these probes, in
which the U(2) matrix describing the embedding is diagonal. The fluctuations of
the brane probes correspond to the mesons. In particular, the off-diagonal
elements of the U(2) fluctuation matrix correspond to the heavy-light mesons,
while the diagonal elements correspond to the light-light and heavy-heavy
mesons, respectively. The heavy-light mesons scale differently with the 't
Hooft coupling than the mesons involving quarks of equal mass. The model
describes both scalar and vector mesons. For different dilaton-deformed gravity
backgrounds, we also calculate the Wilson loop energy, and compare with the
meson masses.Comment: 21 pages, 7 figure
Generalizations of the AdS/CFT correspondence
We consider generalizations of the AdS/CFT correspondence in which probe
branes are embedded in gravity backgrounds dual to either conformal or
confining gauge theories. These correspond to defect conformal field theories
(dCFT) or QCD-like theories with fundamental matter, respectively. Computing
the quark condensate and the meson spectrum for a non-supersymmetric QCD-like
theory from supergravity, we find spontaneous U(1) chiral symmetry breaking as
well as the associated Goldstone boson. For another example at finite
temperature, we observe a phase transition corresponding to a geometrical
transition of the brane embedding. Moreover, starting from the dCFT we discuss
the deconstruction of intersecting M5-branes. The resulting theory corresponds
to two six-dimensional (2,0) superconformal field theories which we show to
have tensionless strings on their four-dimensional intersection. Finally, we
comment on the deconstruction of M-theory from a non-supersymmetric quiver
gauge theory.Comment: Ph.D. Thesis, Humboldt University, Berlin, 130 pages, 38 figures,
accepted for publication in Fortschritte der Physi
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
From Poincare to affine invariance: How does the Dirac equation generalize?
A generalization of the Dirac equation to the case of affine symmetry, with
SL(4,R) replacing SO(1,3), is considered. A detailed analysis of a Dirac-type
Poincare-covariant equation for any spin j is carried out, and the related
general interlocking scheme fulfilling all physical requirements is
established. Embedding of the corresponding Lorentz fields into
infinite-component SL(4,R) fermionic fields, the constraints on the SL(4,R)
vector-operator generalizing Dirac's gamma matrices, as well as the minimal
coupling to (Metric-)Affine gravity are studied. Finally, a symmetry breaking
scenario for SA(4,R) is presented which preserves the Poincare symmetry.Comment: 34 pages, LaTeX2e, 8 figures, revised introduction, typos correcte
A Higgs Mechanism for Gravity
In this paper we elaborate on the idea of an emergent spacetime which arises
due to the dynamical breaking of diffeomorphism invariance in the early
universe. In preparation for an explicit symmetry breaking scenario, we
consider nonlinear realizations of the group of analytical diffeomorphisms
which provide a unified description of spacetime structures. We find that
gravitational fields, such as the affine connection, metric and coordinates,
can all be interpreted as Goldstone fields of the diffeomorphism group. We then
construct a Higgs mechanism for gravity in which an affine spacetime evolves
into a Riemannian one by the condensation of a metric. The symmetry breaking
potential is identical to that of hybrid inflation but with the non-inflaton
scalar extended to a symmetric second rank tensor. This tensor is required for
the realization of the metric as a Higgs field. We finally comment on the role
of Goldstone coordinates as a dynamical fluid of reference.Comment: 15 pages, 2 figures, 3 tables, appendix C on on-shell d.o.f. added,
references adde
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