133 research outputs found
Supersymmetric Branes on AdS_5 x Y^{p,q} and their Field Theory Duals
We systematically study supersymmetric embeddings of D-brane probes of
different dimensionality in the AdS_5xY^{p,q} background of type IIB string
theory. The main technique employed is the kappa symmetry of the probe's
worldvolume theory. In the case of D3-branes, we recover the known three-cycles
dual to the dibaryonic operators of the gauge theory and we also find a new
family of supersymmetric embeddings. The BPS fluctuations of dibaryons are
analyzed and shown to match the gauge theory results. Supersymmetric
configurations of D5-branes, representing domain walls, and of spacetime
filling D7-branes (which can be used to add flavor) are also found. We also
study the baryon vertex and some other embeddings which break supersymmetry but
are nevertheless stable.Comment: LaTeX, 2 figures, 54 pages; v2: discussions sharpened at several
points, new subsection and references adde
Localized Backreacted Flavor Branes in Holographic QCD
We investigate the perturbative (in ) backreaction of localized
D8 branes in D4-D8 systems including in particular the Sakai Sugimoto model. We
write down the explicit expressions of the backreacted metric, dilaton and RR
form. We find that the backreaction remains small up to a radial value of , and that the background functions are smooth except
at the D8 sources. In this perturbative window, the original embedding remains
a solution to the equations of motion. Furthermore, the fluctuations around the
original embedding, describing scalar mesons, do not become tachyonic due to
the backreaction in the perturbative regime. This is is due to a cancelation
between the DBI and CS parts of the D8 brane action in the perturbed
background.Comment: 1+48 pages (7 figures) + 15 pages, citations added & minor
correction
On unquenched N=2 holographic flavor
The addition of fundamental degrees of freedom to a theory which is dual (at
low energies) to N=2 SYM in 1+3 dimensions is studied. The gauge theory lives
on a stack of Nc D5 branes wrapping an S^2 with the appropriate twist, while
the fundamental hypermultiplets are introduced by adding a different set of Nf
D5-branes. In a simple case, a system of first order equations taking into
account the backreaction of the flavor branes is derived (Nf/Nc is kept of
order 1). From it, the modification of the holomorphic coupling is computed
explicitly. Mesonic excitations are also discussed.Comment: 25 pages, 4 figure
Mesons in marginally deformed AdS/CFT
We study the embedding of spacetime filling D7-branes in beta-deformed
backgrounds which, according to the AdS/CFT dictionary, corresponds to
flavoring beta-deformed N=4 super Yang-Mills. We consider supersymmetric and
more general non-supersymmetric three parameter deformations. The equations of
motion for quadratic fluctuations of a probe D7-brane wrapped on a deformed
three-sphere exhibit a non-trivial coupling between scalar and vector modes
induced by the deformation. Nevertheless, we manage to solve them analytically
and find that the mesonic mass spectrum is discrete, with a mass gap and a
Zeeman-like splitting occurs. Finally we propose the action for the dual field
theory as obtained by star-product deformation of super Yang-Mills with
fundamental matter.Comment: LaTex, 42 pages, 3 figures, uses JHEP
A note on fermions in holographic QCD
We study the fermionic sector of a probe D8-brane in the supergravity
background made of D4-branes compactified on a circle with supersymmetry broken
explicitly by the boundary conditions. At low energies the dual field theory is
effectively four-dimensional and has proved surprisingly successful in
recovering qualitative and quantitative properties of QCD. We investigate
fluctuations of the fermionic fields on the probe D8-brane and interpret these
as mesinos (fermionic superpartners of mesons). We demonstrate that the masses
of these modes are comparable to meson masses and show that their interactions
with ordinary mesons are not suppressed.Comment: 21+1 pp, 1 figure; v2: typos corrected, refs. adde
Spectroscopy of fermionic operators in AdS/CFT
We compute the spectrum of color-singlet fermionic operators in the N=2 gauge
theory on intersecting D3 and D7-branes using the AdS/CFT correspondence. The
operator spectrum is found analytically by solving the equations for the dual
D7-brane fluctuations. For the fermionic part of the D7-brane action, we use
the Dirac-like form found by Martucci et al. (hep-th/0504041). We also consider
the baryon spectrum of a large class of supersymmetric gauge theories using a
phenomenological approach to the gauge/gravity duality.Comment: 19 pages, 2 tables, references adde
Cascading Quivers from Decaying D-branes
We use an argument analogous to that of Kachru, Pearson and Verlinde to argue
that cascades in L^{a,b,c} quiver gauge theories always preserve the form of
the quiver, and that all gauge groups drop at each step by the number M of
fractional branes. In particular, we demonstrate that an NS5-brane that sweeps
out the S^3 of the base of L^{a,b,c} destroys M D3-branes.Comment: 11 pages, 1 figure; v2: references adde
Holographic Gauge Theories in Background Fields and Surface Operators
We construct a new class of supersymmetric surface operators in N=4 SYM and
find the corresponding dual supergravity solutions. We show that the insertion
of the surface operator - which is given by a WZW model supported on the
surface - appears by integrating out the localized degrees of freedom along the
surface which arise microscopically from a D3/D7 brane intersection.
Consistency requires constructing N=4 SYM in the D7 supergravity background and
not in flat space. This enlarges the class of holographic gauge theories dual
to string theory backgrounds to gauge theories in non-trivial supergravity
backgrounds. The dual Type IIB supergravity solutions we find reveal - among
other features - that the holographic dual gauge theory does indeed live in the
D7-brane background.Comment: 42 pages, harvmac, corrected typo
Sakai-Sugimoto model, Tachyon Condensation and Chiral symmetry Breaking
We modify the Sakai-Sugimoto model of chiral symmetry breaking to take into
account the open string tachyon which stretches between the flavour D8-branes
and anti D8-branes. There are several reasons of consistency for doing this:
(i) Even if it might be reasonable to ignore the tachyon in the ultraviolet
where the flavour branes and antibranes are well separated and the tachyon is
small, it is likely to condense and acquire large values in the infrared where
the branes meet. This takes the system far away from the perturbatively stable
minimum of the Sakai-Sugimoto model; (ii) The bifundamental coupling of the
tachyon to fermions of opposite chirality makes it a suitable candidate for the
quark mass and chiral condensate parameters. We show that the modified
Sakai-Sugimoto model with the tachyon present has a classical solution
satisfying all the desired consistency properties. In this solution chiral
symmetry breaking coincides with tachyon condensation. We identify the
parameters corresponding to the quark mass and the chiral condensate and also
briefly discuss the mesonic spectra.Comment: 18 pages, latex; v3; conclusion in subsection 3.1 modified and
appropriate changes made in the abstract and introduction to reflect this;
typos corrected; version to appear in JHE
- âŠ