STRINGY EVIDENCE FOR D=11 STRUCTURE IN A STRONGLY COUPLED TYPE-IIA SUPERSTRING

Witten proposed that the low energy physics of a strongly coupled D = 10 type-IIA superstring may be described by D = 11 supergravity. To ex plore the stringy aspects of the underlying theory we examine the stri ngy massive states. We propose a systematic formula for identifying no nperturbative states in D = 10 type-IIA superstring theory, such that, together with the elementary excited string states, they form D = 11 supersymmetric multiplets, in SO(10) representations. This provides hi nts for the construction of a conjectured weakly coupled D = 11 theory that is dual to the strongly coupled D = 10 type-IIA superstring.