Developments in superstring field theory

In this article the structure of superstring theories is outlined. The one-loop quantum superstring gauge anomalies are then described and it is shown that their absence leads to an interesting theory with gauge group SO(32). The one-loop infinities also cancel for this gauge group. The anomaly cancellation can be understood in terms of the low-energy effective supergravity-Yang-Mills field theory, from which it is shown that E8 x E8 is an equally good gauge group, which suggests that there should also be an interesting E8 x E8 superstring theory. A new type of superstring theory, known as the 'heterotic' string theory, which only describes strings with gauge groups E8 x E8 or SO(32) is described. Finally some very exciting prospects for obtaining a sensible description of four-dimensional physics from a ten-dimensional superstring theory with gauge group E8 x E8 is outlined. (author)