BRST quantization in anti-de Sitter space

We discuss the status of the superstring theory on ad S/sub 5/*S/sup 5/ space and difficulties with its quantization due to the nonlinear realization of the SU(2,2 4) superconformal symmetry. We propose a toy model in two dimensions where this symmetry is realized linearly and supertwistors are used as `quarks' of this supergroup. A possible relation between the string theory and the toy model is studied in the case of a massive particle propagating in AdS/sub 5/ space: a generalized twistor construction is shown to lead to a quadratic action and simple BRST quantization. We hope that these results will help to also eventually quantize the string on ad S/sub 5/*S/sup 5/. (10 refs).