647 research outputs found
RG Flows Towards IR Isolated Fixed Points: Some Type 0 Samples
We perform here a critical analysis of some non-supersymmetric gravity
solutions in Type 0B string theory. We first consider the most general
configuration of parallel N electric and M magnetic D3-branes. The field theory
living on their worldvolume is non-supersymmetric and non-conformal (if N is
different from M) and has gauge group SU(N)XSU(M). We study the IR regime of
the conjectured dual gravity background. A fine tuned solution exists with an
asymptotically vanishing tachyon and a running dilaton, which could correspond
to a flow towards an IR isolated fixed point at strong coupling. This opens the
question upon the possibility of extending AdS/CFT techniques to flows towards
IR isolated fixed points. We then use D3-branes as probes of this and other
Type 0 backgrounds available in literature which cover the M=0 (or N=0) case.
We shaw that for the fine tuned IR conformal solutions the stacks of parallel
branes are plagued by instabilities, due to the repulsive force between branes
of the same type. Curiously, for a particular solution which could be dual to a
confining gauge theory, the stack should instead be stable.Comment: 19 pages, LateX; version revised for publication in JHE
Holographic duals of SQCD models in low dimensions
We obtain gravity duals to supersymmetric gauge theories in two and three
spacetime dimensions with unquenched flavor. The supergravity solutions are
generated by a set of color branes wrapping a compact cycle in a Calabi-Yau
threefold, together with another set of flavor branes extended along the
directions orthogonal to the cycle wrapped by the color branes. We construct
supergravity backgrounds which include the backreaction induced by a smeared
set of flavor branes, which act as delocalized dynamical sources of the
different supergravity fields.Comment: 42 pages, 5 figures;v2: typos correcte
D3-D7 Quark-Gluon Plasmas at Finite Baryon Density
We present the string dual to SU(Nc) N=4 SYM, coupled to Nf massless
fundamental flavors, at finite temperature and baryon density. The solution is
determined by two dimensionless parameters, both depending on the 't Hooft
coupling at the scale set by the temperature T:
, weighting the backreaction of the flavor
fields and , where is the
baryon density. For small values of these two parameters the solution is given
analytically up to second order. We study the thermodynamics of the system in
the canonical and grand-canonical ensembles. We then analyze the energy loss of
partons moving through the plasma, computing the jet quenching parameter and
studying its dependence on the baryon density. Finally, we analyze certain
"optical" properties of the plasma. The whole setup is generalized to non
abelian strongly coupled plasmas engineered on D3-D7 systems with D3-branes
placed at the tip of a generic singular Calabi-Yau cone. In all the cases,
fundamental matter fields are introduced by means of homogeneously smeared
D7-branes and the flavor symmetry group is thus a product of abelian factors.Comment: 27 pages; v2: 29 pages, 1 (new) figure, new section 4.4 on optical
properties, references, comments added; v3: eq. (3.19), comments and a
reference adde
Consistent reduction of charged D3-D7 systems
We provide a consistent reduction to five dimensions of the system of
D3-branes at Calabi-Yau singularities coupled to D7-branes with world-volume
gauge flux. The D3-branes source the dual to would-be conformal quiver
theories. The D7-branes, which are homogeneously distributed in their
transverse directions, are dual to massless matter in the fundamental
representation at finite (baryon) density. We provide the five-dimensional
action and equations of motion, and discuss a few sub-truncations. The
reduction can be used in the study of transport properties and stability of
D3-D7 charged systems.Comment: 23 pages. v2: references added and minor change
N=2 Gauge Theories from Wrapped Five-branes
We present string duals of four dimensional N=2 pure SU(N) SYM theory. The
theory is obtained as the low energy limit of D5-branes wrapped on non-trivial
two-cycles. Using seven dimensional gauged supergravity and uplifting the
result to ten dimensions, we obtain solutions corresponding to various points
of the N=2 moduli space. The more symmetric solution may correspond to a point
with rotationally invariant classical vevs. By turning on seven dimensional
scalar fields, we find a solution corresponding to a linear distribution of
vevs. Both solutions are conveniently studied with a D5-probe, which also
confirms many of the standard expectations for N=2 solutions.Comment: 11 pages, LateX. Revised versio
Gravity duals of 2d supersymmetric gauge theories
We find new supergravity solutions generated by D5-branes wrapping a
four-cycle and preserving four and two supersymmetries. We first consider the
configuration in which the fivebranes wrap a four-cycle in a Calabi-Yau
threefold, which preserves four supersymmetries and is a gravity dual to the
Coulomb branch of two-dimensional gauge theories with N=(2,2) supersymmetry. We
also study the case of fivebranes wrapping a co-associative four-cycle in a
manifold of G_2-holonomy, which provides a gravity dual of N=(1,1)
supersymmetric Yang-Mills theory in two dimensions. We also discuss the
addition of unquenched fundamental matter fields to these backgrounds and find
the corresponding gravity solutions with flavor brane sources.Comment: 34 pages + appendices; v2: minor improvement
Splitting of macroscopic fundamental strings in flat space and holographic hadron decays
In this review article we present the calculation of the splitting rate in
flat space of a macroscopic fundamental string either intersecting at a generic
angle a Dp-brane or lying on it. The result is then applied, in the context of
the string/gauge theory correspondence, to the study of exclusive decay rates
of large spin mesons into mesons. As examples, we discuss the cases of N=4 SYM
with a small number of flavors, and of QCD-like theories in the quenched
approximation. In the latter context, explicit analytic formulas are given for
decay rates of mesons formed either by heavy quarks or by massless quarks.Comment: 17 pages, 3 figures. Invited review for Modern Physics Letters
Supersymmetry breaking at the end of a cascade of Seiberg dualities
We study the IR dynamics of the cascading non-conformal quiver theory on N
regular and M fractional D3 branes at the tip of the complex cone over the
first del Pezzo surface. The horizon of this cone is the irregular
Sasaki-Einstein manifold Y^{2,1}. Our analysis shows that at the end of the
cascade supersymmetry is dynamically broken.Comment: 12 pages, 2 figures, minor changes, typos correcte
Holographic Duals of Quark Gluon Plasmas with Unquenched Flavors
We review the construction of gravitational solutions holographically dual to
N=1 quiver gauge theories with dynamical flavor multiplets. We focus on the
D3-D7 construction and consider the finite temperature, finite quark chemical
potential case where there is a charged black hole in the dual solution.
Discussed physical outputs of the model include its thermodynamics (with
susceptibilities) and general hydrodynamic properties.Comment: Lecture presented at the Workshop "AdS/CFT and Novel Approaches to
Hadron and Heavy Ion Physics", Kavli Institute of Theoretical Physics
(KITPC), Beijing, China, 13 October 2010. Review article to be published in
Communications in Theoretical Physics. 27 pages, 2 figure
Strings on pp-waves and Hadrons in (softly broken) N=1 gauge theories
We study the Penrose limit of Type IIB duals of softly broken N=1 SU(N) gauge
theories in four dimensions, obtained as deformations of the Maldacena-Nunez
and Klebanov-Strassler backgrounds. We extract the string spectrum on the
resulting pp-wave backgrounds and discuss some properties of the conjectured
dual gauge theory hadrons, the so called "Annulons". The string zero-point
energy on the light-cone is nontrivial, due to the loss of linearly realized
worldsheet supersymmetry, and negative, even in the unbroken supersymmetric
case. This causes the appearance of non-perturbative corrections to the
hadronic mass spectrum. We briefly discuss the thermodynamic behavior of these
string models, calculating the corresponding Hagedorn temperatures.Comment: 20 page
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