Alfonso V. Ramallo

Backreacting flavors in the Klebanov-Strassler background

In this paper we present new analytic solutions of pure Type IIB supergravity plus D7-branes describing the addition of an arbitrary number of flavors to the Klebanov-Tseytlin and Klebanov-Strassler backgrounds. We provide a precise field theory dual and a detailed analysis of the duality cascade which describes its RG flow. Matchings of beta functions and anomalies between the field theory and the string setup are presented. We give an understanding of Seiberg duality as a large gauge transformation on the RR and NSNS potentials. We also analyze the UV behavior of the field theory that, as suggested by the string background, can be associated with a duality wall.

Unquenched flavors in the Klebanov-Witten model

Using AdS/CFT, we study the addition of an arbitrary number of backreacting flavors to the Klebanov-Witten theory, making many checks of consistency between our new Type IIB plus branes solution and expectations from field theory. We study generalizations of our method for adding flavors to all = 1 SCFTs that can be realized on D3-branes at the tip of a Calabi-Yau cone. Also, general guidelines suitable for the addition of massive flavor branes are developed.

Flavoring the gravity dual of Script N = 1 Yang-Mills with probes

We study two related problems in the context of a supergravity dual to = 1 SYM. One of the problems is finding kappa symmetric D5-brane probes in this particular background. The other is the use of these probes to add flavors to the gauge theory. We find a rich and mathematically appealing structure of the supersymmetric embeddings of a D5-brane probe in this background. Besides, we compute the mass spectrum of the low energy excitations of = 1 SQCD (mesons) and match our results with some field theory aspects known from the study of supersymmetric gauge theories with a small number of flavors.

Unquenched Flavor in the Gauge/Gravity Correspondence

Within the AdS/CFT correspondence, we review the studies of field theories with a large number of adjoint and fundamental fields, in the Veneziano limit. We concentrate in set-ups where the fundamentals are introduced by a smeared set of D-branes. We make emphasis on the general ideas and then in subsequent chapters that can be read independently and describe particular considerations in various different models. Some new material is presented along the various sections.

Supersymmetric probes on the conifold

We study the supersymmetric embeddings of different D-brane probes in the AdS5 ? T1,1 geometry. The main tool employed is kappa symmetry and the cases studied include D3-, D5- and D7-branes. We find a family of three-cycles of the T1,1 space over which a D3-brane can be wrapped supersymmetrically and we determine the field content of the corresponding gauge theory duals. Supersymmetric configurations of D5-branes wrapping a two-cycle and of spacetime filling D7-branes are also found. The configurations in which the entire T1,1 space is wrapped by a D5-brane (baryon vertex) and a D7-brane are also studied. Some other embeddings which break supersymmetry but are nevertheless stable are also determined.

Stable wrapped branes

We study some wrapped configurations of branes in the near-horizon geometry of a stack of other branes. The common feature of all the cases analyzed is a quantization rule and the appearance of a finite number of static configurations in which the branes are partially wrapped on spheres. The energy of these configurations can be given in closed form and the analysis of their small oscillations shows that they are stable. The cases studied include D(8−p)-branes in the type-II supergravity background of Dp-branes for 0 ≤ p ≤ 5, M5-branes in the M5-brane geometry in M-theory and D3-branes in a (p,q) fivebrane background in the type-IIB theory. The brane configurations found admit the interpretation of bound states of strings (or M2-branes in M-theory) which extend along the unwrapped directions. We check this fact directly in a particular case by using the Myers polarization mechanism.

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.

Supersymmetric branes on AdS5 × Yp,q and their field theory duals

We systematically study supersymmetric embeddings of D-brane probes of different dimensionality in the AdS5 × Y p,q background of type IIB string theory. The main technique employed is the kappa symmetry of the probes 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.

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 = 1 supersymmetric Maldacena-Nunez background.

High energy nucleus-nucleus collisions in the dual parton model

Abstract Average multiplicities, rapidity densities and dispersion in high-energy nucleus-nucleus collisions are computed in the framework of the dual parton model. Particular attention is devoted to the case of central collision, especially in connection with the possible production of a quark-gluon plasma. Our results are compared with recent cosmic ray data. A comparison of the predictions of different models is also given.