26 research outputs found
Mesons in gauge/gravity dual with large number of fundamental fields
In view of extending gauge/gravity dualities with flavour beyond the probe
approximation, we establish the gravity dual description of mesons for a
three-dimensional super Yang-Mills theory with fundamental matter. For this
purpose we consider the fully backreacted D2/D6 brane solution of Cherkis and
Hashimoto in an approximation due to Pelc and Siebelink. The low-energy field
theory is the IR fixed point theory of three-dimensional N=4 SU(N_c) super
Yang-Mills with N_f fundamental fields, which we consider in a large N_c and
N_f limit with N_f/N_c finite and fixed. We discuss the dictionary between
meson-like operators and supergravity fluctuations in the corresponding
near-horizon geometry. In particular, we find that the mesons are dual to the
low-energy limit of closed string states. In analogy to computations of
glueball mass spectra, we calculate the mass of the lowest-lying meson and find
that it depends linearly on the quark mass.Comment: 19 pages, LaTeX, 6 figures, v2: fig. 4 added, refs. adde
Adding flavor to the gravity dual of non-commutative gauge theories
We study the addition of flavor degrees of freedom to the supergravity dual
of the non-commutative deformation of the maximally supersymmetric gauge
theories. By considering D7 flavor branes in the probe approximation and
studying their fluctuations we extract the spectrum of scalar and vector mesons
as a function of the non-commutativity. We find that the spectrum for very
large non-commutative parameter is equal to the one in the commutative theory,
while for some intermediate values of the non-commutativity some of the modes
disappear from the discrete spectrum. We also study the semiclassical dynamics
of rotating open strings attached to the D7-brane, which correspond to mesons
with large spin. Under the effect of the non-commutativity the open strings get
tilted. However, at small(large) distances they display the same Regge-like
(Coulombic) behaviour as in the commutative theory. We also consider the
addition of D5-flavor branes to the non-commutative deformation of the N=1
supersymmetric Maldacena-Nunez background.Comment: 50 pages, 9 figures, LaTeX; v2: minor improvements, references added;
v3: typos correcte
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
Fundamental matter, meson spectroscopy and non-critical string/gauge duality
We discuss the incorporation of quarks in the fundamental representation of
the color group into the non-critical string/gauge duality. We focus on
confining theories and address this question using two different approaches:
(i) by introducing flavor probe branes and (ii) by deriving backreacted
flavored near extremal gravity backgrounds. In the former approach we analyze
the near extremal AdS_6 model with D4 and anti-D4 probe flavor branes included.
We study the meson spectrum and discuss the role played by the constituent
quark mass, related to the integration constant that defines the embedding. As
for the second approach we derive a class of flavored AdS_{n+1} x S^k black
hole solutions. In particular we write down the flavored AdS_6 and AdS_5 black
holes and the near extremal AdS_5 x S^1 backgrounds. We analyze several gauge
dynamical properties associated with these models.Comment: 46 pages, 7 figures. v.2: some references and a comment about the
comparison with analogous critical models were added. v.3: a comment added;
published versio
Open string modes at brane intersections
We study systematically the open string modes of a general class of BPS
intersections of branes. We work in the approximation in which one of the
branes is considered as a probe embedded in the near-horizon geometry generated
by the other type of branes. We mostly concentrate on the D3-D5 and D3-D3
intersections, which are dual to defect theories with a massive hypermultiplet
confined to the defect. In these cases we are able to obtain analytical
expressions for the fluctuation modes of the probe and to compute the
corresponding mass spectra of the dual operators in closed form. Other BPS
intersections are also studied and their fluctuation modes and spectra are
found numerically.Comment: 58 pages, 3 figures, LaTeX;v2: typos correcte
Holographic mesons in various dimensions
We calculate the spectrum of fluctuations of a probe Dk-brane in the
background of N Dp-branes, for k=p,p+2,p+4 and p< 5. The result corresponds to
the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory
coupled to `dynamical quarks', i.e., fields in the fundamental representation
-- the latter are confined to a defect for k=p and p+2. We find a universal
behaviour where the spectrum is discrete and the mesons are deeply bound. The
mass gap and spectrum are set by the scale M ~ m_q/g_{eff}(m_q), where m_q is
the mass of the fundamental fields and g_{eff}(m_q) is the effective coupling
evaluated at the quark mass, i.e. g_{eff}^2(m_q)=g_{ym}^2 N m_q^{p-3}. We
consider the evolution of the meson spectra into the far infrared of
three-dimensional SYM, where the gravity dual lifts to M-theory. We also argue
that the mass scale appearing in the meson spectra is dictated by holography.Comment: 44 pages, 2 figures; v2: typos corrected, references adde
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
Holographic flavor on the Higgs branch
In this paper we study the holographic dual, in several spacetime dimensions,
of the Higgs branch of gauge theories with fundamental matter. These theories
contain defects of various codimensionalities, where the matter fields are
located. In the holographic description the matter is added by considering
flavor brane probes in the supergravity backgrounds generated by color branes,
while the Higgs branch is obtained when the color and flavor branes recombine
with each other. We show that, generically, the holographic dual of the Higgs
phase is realized by means of the addition of extra flux on the flavor branes
and by choosing their appropriate embedding in the background geometry. This
suggests a dielectric interpretation in terms of the color branes, whose vacuum
solutions precisely match the F- and D-flatness conditions obtained on the
field theory side. We further compute the meson mass spectra in several cases
and show that when the defect added has codimension greater than zero it
becomes continuous and gapless.Comment: 59 pages, 1 figure;v2: references adde
Long-range Angular Correlations On The Near And Away Side In P-pb Collisions At âsnn=5.02 Tev
7191/Mar294
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Direct observation of the growth of voids in multifilamentary superconducting materials via hot stage scanning electron microscopy
The need for large high field magnetic devices has focused attention on multifilamentary superconductors based on A15 compounds such as Nb/sub 3/Sn. The commercial bronze process for fabricating multifilamentary superconducting Nb/sub 3/Sn wires was developed. A major problem is strain sensitivity when long reaction times are employed. An improved hot stage for the scanning electron microscope was constructed to study the formation of the A15 phase by solid state diffusion. The nucleation and growth of voids near the interface of the A15 phase (Nb/sub 3/Sn) and matrix were observed, monitored, and recorded on video tape. Successive layers of material heated in the hot stage were subsequently removed and the new surfaces were re-examined, using SEM-EDX and optical microscopy, to confirm the fact that the observed porosity was indeed a bulk rather than a surface phenomenon. These voids are considered to be a primary cause for degrading the mechanical, thermal and superconducting properties