Matrix string states in pure 2d Yang-Mills theories

We quantize pure 2d Yang-Mills theory on a torus in the gauge where the fie ld strength is diagonal. Because of the topological obstructions to a globa l smooth diagonalization, we find string-like states in the spectrum simila r to the ones introduced by various authors in Matrix string theory. We wri te explicitly the partition function, which generalizes the one already kno wn in the literature, and we discuss the role of these states in preserving modular invariance. Some speculations are presented about the interpretati on of 2d Yang-Mills theory as a Matrix string theory. (C) 1999 Published by Elsevier Science B.V.