A note on six-dimensional gauge theories

We study the new “gauge” theories in 5+1 dimensions, and their non-commutative generalizations. We argue that the θ-term and the non-commutative torus parameters appear on an equal footing in the non-critical string theories which define the gauge theories. The use of these theories as a Matrix description of M-theory on T5, as well as a closely related realization as 5-branes in type IIB string theory, proves useful in studying some of their properties.