Some Properties of Type I String Theory

I am pleased to contribute to this volume in memory of Yuri Golfand. His name will be remembered by future generations of physicists for his 1971 paper with Likhtman, which introduced the four-dimensional super-Poincaré algebra for the first time. Recognizing that such a symmetry algebra is a consistent mathematical possibility was certainly a remarkable achievement. It is a curious coincidence that this paper appeared within a few days of Pierre Ramond’s paper on fermionic strings. Communications were not so good in those days, and the Golfand–Likhtman work was not generally known (at least in the West) for several years. As a result, its influence in driving the development of supersymmetry was not as great as it should have been. In fact, supersymmetric theories in two dimensions were developed to describe the world-sheet theory of RNS strings, and this motivated Wess and Zumino to seek fourdimensional analogs. Only years later did we understand that RNS strings, properly interpreted, have local 10-dimensional spacetime supersymmetry. The version of the theory that received the most attention prior to 1985 was the one containing both open and closed strings, which Mike Green and I called the type I theory, since it has one ten-dimensional supersymmetry. In 1984 we showed that this theory is inconsistent (due to gauge anomalies) unless the gauge group is chosen to be SO(32). Then the anomalies cancel, and consistency is achieved. In this manuscript, I propose to review some of the interesting features that appear when one of the spatial dimensions is chosen to be a circle. In this case an alternative T dual description, known as type I, is available. This description gives a different viewpoint for understanding various phenomena, such as gauge symmetry enhancement. The material presented here is not new, though it may be organized somewhat differently than has been done before.