On Penrose limits and gauge Theories

We discuss various Penrose limits of conformal and nonconformal backgrounds.In AdS_5 x T^{1,1}, for a particular choice of the angular coordinate inT^{1,1} the resulting Penrose limit coincides with the similar limit for AdS_5x S^5. In this case an identification of a subset of field theory operatorswith the string zero modes creation operators is possible. For another limit weobtain a light-cone string action that resembles a particle in a magneticfield. We also consider three different types of backgrounds that are dual tononconformal field theories: The Schwarzschild black hole in AdS_5, D3-braneson the small resolution of the conifold and the Klebanov-Tseytlin background.We find that in all three cases the introduction of nonconformality renders atheory that is no longer exactly solvable and that the form of the deformationis universal. The corresponding world sheet theory in the light-cone gauge hasa \tau=x^+ dependent mass term.Comment: 17pp, late