On the Consistency of Null Strings Literature: The Tale of an Overlooked Symmetry

Abstract

We observe that the null string action possesses a previously overlooked local symmetry. By correctly accounting for this symmetry, we show that the number of physical propagating degrees of freedom of null strings in $D$ dimensional target space is $D-3$, in contrast to $D-2$ that one finds in the literature. Overlooking this symmetry has led to an unphysical over-counting of states, rendering the null string analyses inconsistent. Thus, our observation calls for a thorough revision of all statements and results in the null string literature.