Hi! I am a bit confused about the AdS/CFT conjecture.... One of the things I don't really understand is when N=4 SYM is a valid description of the D-brane dynamics. My impression was this: In the open string picture of branes, the massless excitations of the open string connected to the brane leads to the SYM. But at high energy, massive excitations will appear and the SYM will no longer give a complete description, i.e. the field theory limit is no longer valid. However, when I read superficially through the AdS/CFT-literature, the argument goes that for D3-branes, the SYM is superconformal and therefore a valid description of the brane at any energy. Is this somehow related to the near-horizon limit? Any answers would be greatly appreciated!