Little theories in six and seven dimensions Original Research Article

We discuss theories with 16 and 8 supercharges in six and seven dimensions. These theories are defined as world-volume theories of -5- and 6-branes of type 11 and M theories, in the limit in which bulk modes decouple. We analyze in detail the spectrum of BPS extended objects of these theories, and show that the six-dimensional ones can be interpreted as little (non-critical) string theories. The little 5-branes of the six-dimensional theories with 16 supercharges are used to find new string theories with 8 supercharges, which have additional group structure. We describe the web of dualities relating all these theories. We show that the theories with 16 supercharges can be used for a Matrix description of M-theory on T6 in the general case, and that they also reproduce Matrix theory on T5 and T4 in some particular limit.