50 research outputs found
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
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 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
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
Towards an Explicit Model of D-brane Inflation
We present a detailed analysis of an explicit model of warped D-brane
inflation, incorporating the effects of moduli stabilization. We consider the
potential for D3-brane motion in a warped conifold background that includes
fluxes and holomorphically-embedded D7-branes involved in moduli stabilization.
Although the D7-branes significantly modify the inflaton potential, they do not
correct the quadratic term in the potential, and hence do not cause a uniform
change in the slow-roll parameter eta. Nevertheless, we present a simple
example based on the Kuperstein embedding of D7-branes, z_1=constant, in which
the potential can be fine-tuned to be sufficiently flat for inflation. To
derive this result, it is essential to incorporate the fact that the
compactification volume changes slightly as the D3-brane moves. We stress that
the compactification geometry dictates certain relationships among the
parameters in the inflaton Lagrangian, and these microscopic constraints impose
severe restrictions on the space of possible models. We note that the shape of
the final inflaton potential differs from projections given in earlier studies:
in configurations where inflation occurs, it does so near an inflection point.
Finally, we comment on the difficulty of making precise cosmological
predictions in this scenario. This is the companion paper to arXiv:0705.3837.Comment: 68 pages, 6 figures; v2: fixed typos, added refs and clarifications;
v3: expanded discussion of inflection point inflatio
Irresponsiveness of two retinoblastoma cases to conservative therapy correlates with up- regulation of hERG1 channels and of the VEGF-A pathway
<p>Abstract</p> <p>Background</p> <p>Treatment strategies for Retinoblastoma (RB), the most common primary intraocular tumor in children, have evolved over the past few decades and chemoreduction is currently the most popular treatment strategy. Despite success, systemic chemotherapeutic treatment has relevant toxicity, especially in the pediatric population. Antiangiogenic therapy has thus been proposed as a valuable alternative for pediatric malignancies, in particolar RB. Indeed, it has been shown that vessel density correlates with both local invasive growth and presence of metastases in RB, suggesting that angiogenesis could play a pivotal role for both local and systemic invasive growth in RB. We present here two cases of sporadic, bilateral RB that did not benefit from the conservative treatment and we provide evidence that the VEGF-A pathway is significantly up-regulated in both RB cases along with an over expression of hERG1 K<sup>+ </sup>channels.</p> <p>Case presentation</p> <p>Two patients showed a sporadic, bilateral RB, classified at Stage II of the Reese-Elsworth Classification. Neither of them got benefits from conservative treatment, and the two eyes were enucleated. In samples from both RB cases we studied the VEGF-A pathway: VEGF-A showed high levels in the vitreous, the <it>vegf-a, flt-1, kdr</it>, and <it>hif1-α </it>transcripts were over-expressed. Moreover, both the transcripts and proteins of the hERG1 K<sup>+ </sup>channels turned out to be up-regulated in the two RB cases compared to the non cancerous retinal tissue.</p> <p>Conclusions</p> <p>We provide evidence that the VEGF-A pathway is up-regulated in two particular aggressive cases of bilateral RB, which did not experience any benefit from conservative treatment, showing the overexpression of the <it>vegf-a</it>, <it>flt-1</it>, <it>kdr </it>and <it>hif1-α </it>transcripts and the high secretion of VEGF-A. Moreover we also show for the first time that the <it>herg1 </it>gene transcripts and protein are over expressed in RB, as occurs in several aggressive tumors. These results further stress the relevance of the VEGF-A pathway in RB and the correlation with hERG1, making aggressive and recurrent RB cases good candidates for antiangiogenesis therapies based on the targeting of VEGF-A.</p
Spectral functions in V-QCD with matter: masses, susceptibilities, diffusion and conductivity
Brane effective actions, kappa-symmetry and applications
This is a review on brane effective actions, their symmetries and some of their applications. Its first part covers the GreenâSchwarz formulation of single M- and D-brane effective actions focusing on kinematical aspects: the identification of their degrees of freedom, the importance of world volume diffeomorphisms and kappa symmetry to achieve manifest spacetime covariance and supersymmetry, and the explicit construction of such actions in arbitrary on-shell supergravity backgrounds. Its second part deals with applications. First, the use of kappa symmetry to determine supersymmetric world volume solitons. This includes their explicit construction in flat and curved backgrounds, their interpretation as BogomolânyiâPrasadâSommerfield (BPS) states carrying (topological) charges in the supersymmetry algebra and the connection between supersymmetry and Hamiltonian BPS bounds. When available, I emphasise the use of these solitons as constituents in microscopic models of black holes. Second, the use of probe approximations to infer about the non-trivial dynamics of strongly-coupled gauge theories using the anti de Sitter/conformal field theory (AdS/CFT) correspondence. This includes expectation values of Wilson loop operators, spectrum information and the general use of D-brane probes to approximate the dynamics of systems with small number of degrees of freedom interacting with larger systems allowing a dual gravitational description. Its final part briefly discusses effective actions for N D-branes and M2-branes. This includes both Super-Yang-Mills theories, their higher-order corrections and partial results in covariantising these couplings to curved backgrounds, and the more recent supersymmetric ChernâSimons matter theories describing M2-branes using field theory, brane constructions and 3-algebra considerations