In Search of an Easy Witness: Exponential Time vs. Probabilistic Polynomial Time

Restricting the search space f0; 1g n to the set of truth tables of easy Boolean functions on log n variables, as well as using some known hardness-randomness tradeoffs, we establish a number of results relating the complexity of exponential-time and probabilistic polynomial-time complexity classes. In particular, we show that NEXP  P=poly , NEXP = MA; this can be interpreted to say that no derandomization of MA (and, hence, of promise-BPP) is possible unless NEXP contains a hard Boolean function. We also prove several downward closure results for ZPP, RP, BPP, and MA; e.g., we show EXP = BPP , EE = BPE, where EE is the double-exponential time class and BPE is the exponential-time analogue of BPP.