Effective Actions for Heterotic String Theory

Heterotic String Theory is an attempt to construct a description of nature that is more satisfying than the Standard Model. A major problem is that it is very difficult to do explicit calculations in string theory. Therefore, it is useful to construct a 'normal' field theory that approximates HST. The way to construct such a field theory is described briefly. The result is a perturbation expansion in some parameter alpha', related to the inverse string tension. There are problems concerning the supersymmetrisation of the O(alpha'3) contribution. These may be caused by the assumption that the action can be written in terms of a local Lagrangian of the physical fields only.