TOPOLOGY CHANGE AND THETA-VACUA IN 2D YANG-MILLS THEORY

We discuss the existence of theta-vacua in pure Yang-Mills theory in t wo space-time dimensions. More precisely, a procedure is given which a llows one to classify the distinct quantum theories possessing the sam e classical limit for an arbitrary connected gauge group G and compact space-time manifold M (possibly with boundary) possessing a special b asepoint. For any such G and M it is shown that the above quantization s are in one-to-one correspondence with the irreducible unitary repres entations (IUR's) of pi(1)(G) if M is orientable, and with the IUR's o f pi(1)(G)/2 pi(1)(G) if M is non-orientable. (C) 1997 Published by El sevier Science B.V.