On Penrose limits and gauge theories

We discuss various Penrose limits of conformal and nonconformal backgrounds. In AdS₅×T^1,1, for a particular choice of the angular coordinate in T^1,1 the resulting Penrose limit coincides with the similar limit for AdS₅×S⁵. In this case an identification of a subset of field theory operators with the string zero mode creation operators is possible. For another limit we obtain a light-cone string action that resembles a particle in a magnetic field. We also consider three different types of backgrounds that are dual to nonconformal field theories: The Schwarzschild black hole in AdS₅, D3-branes on the small resolution of the conifold and the Klebanov-Tseytlin background. We find that in all three cases the introduction of nonconformality renders a theory that is no longer exactly solvable and that the form of the deformation is universal. The corresponding world sheet theory in the light-cone gauge has a τ = x⁺ dependent mass term.