First they told me it was wrong, then they told me it was obvious.
In this chapter we will formulate the free bosonic string and superstrings as a field theories in their critical dimensions in a way that manifestly possesses Lorentz invariance. While it is to be expected that these theories possess the gauge symmetries of the massless modes we will find that such a formulation of string theory possesses an infinite number of local symmetries. The actions have considerable elegance and make a surprising use of the BRST formalism even though they are classical objects.
One of the most remarkable aspects of the evolution of modern physics has been the central role played by symmetry. The ...