We consider a general framework to study holographically the dynamics of fundamental quarks in a confining gauge theory. Flavors are introduced by placing a set of (coincident) branes and antibranes on a background dual to a confining color theory. The spectrum contains an open string tachyon and its condensation describes the U(N_f)_L x U(N_f)_R -> U(N_f)_V symmetry breaking. By studying worldvolume gauge transformations of the flavor brane action, we obtain the QCD global anomalies and an IR condition that allows to fix the quark condensate in terms of the quark mass. We find the expected N_f^2 Goldstone bosons (for m_q=0), the Gell-Mann-Oakes-Renner relation (for m_q small) and the \eta' mass. Remarkably, the linear confinement behavior for the masses of highly excited spin-1 mesons, m_n^2 ~ n is naturally reproduced.Comment: 30 pages + 5 appendices, 2 figure

We study the String dual to N = 1 SQCD deformed by a quartic superpotential in the quark superfields. We present a unified view of the previous results in the literature and find new exact solutions and new asymptotic solutions. Then we study the Physics encoded in these backgrounds, giving among other things a resolution to an old puzzle related to the beta function and a sufficient criteria for screening. We also extend our results to the SO(N c) case where we present a candidate for the Wilson loop in the spinorial representation. Various aspects of this line of research are critically analyzed. 1

We find non-critical string backgrounds in five and eight dimensions, holographically related to four-dimensional conformal field theories with N = 0 and N = 1 supersymmetries. In the five-dimensional case we find an AdS 5 background metric for a string model related to non-supersymmetric, conformal QCD with large number of colors and flavors and discuss the conjectured existence of a conformal window from the point of view of our solution. In the eight-dimensional string theory, we build a family of solutions of the form AdS 5 ×S 3 withS 3 a squashed three-sphere. For a special value of the ratio N f /N c , the background can be interpreted as the supersymmetric near-horizon limit of a system of color and flavor branes on R 1,3 times a known four-dimensional generalization of the cigar. The N = 1 dual theory with fundamental matter should have an IR fixed point only for a fixed ratio N f /N c . General features of the string/gauge theory correspondence for theories with fundamental flavors are also addressed.

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