Sec. VII. The CSR discussion is extended in Sec. VIII to configuration space. Some final remarks are given in the conclusions in Sec. IX. A check on the validity of CSR is carried out in the Appendix where the results for the g$_{1}$ , V , and MS schemes are confronted in the perturbative domain. The basic principle underlying the AdS/CFT approach to conformal gauge theories is the isomorphism of the group of Poincar´ e and conformal transformations SO (4 , 2) to the group of isometries of AdS$_{5}$ space, the group of transformations that leave the AdS metric invariant ( R the AdS radius). Since the metric (1) is invariant under a dilatation of all coordinates x µ → λx $^{µ}$, z → λz , the variable z acts like a scaling variable in Minkowski space: different values of z correspond to different energy scales at which the hadron is examined. In order to describe a confining theory, the conformal invariance of AdS$_{5}$ must be broken. A simple way to impose confinement and discrete normalizable modes is to truncate the regime where the string modes can propagate by introducing an IR cutoff at a finite value z$_{0}$ ∼ 1 / Λ$_{QCD}$. Thus, the “hard-wall” at z$_{0}$ breaks conformal invariance and allows the introduction of the QCD scale and a spectrum of particle states. [15] In this simplified approach the propagation of hadronic modes in a fixed effective gravitational background encodes the salient properties of the QCD dual theory, such as the ultraviolet (UV) conformal limit at the AdS boundary at z → 0, as well as modifications of the background geometry in the large z infrared region which are dual to confining gauge theories. As first shown by Polchinski and Strassler, [15] the AdS/CFT duality, modified to incorporate a mass scale, provides a derivation of dimensional counting rules [16] for the leading power-law falloff of hard scattering beyond the perturbative regime. The modified theory generates the hard behavior expected from QCD, instead of the soft behavior characteristic of strings. The conformal metric of AdS space can be modified within the AdS/QCD framework to simulate confinement forces. [17] The introduction of a dilaton profile in the AdS action can be considered equivalent to modifying the AdS metric (1) by introducing an additional warp II. LIGHT-FRONT HOLOGRAPHY AND QCD 4 ds 2 = R 2 z 2 ( η$_{µν}$dx $^{µ}$dxν − dz $^{2}$) , (1)