Thickening the string. II. The null-string dust
John J. Stachel · Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields · 1980
The bivector field approach previously applied to a perfect dust of timelike strings is applied to a dust of null strings. The conservation law for the null-string-dust stress-energy tensor is used to prove that each null-string world sheet is ruled by a family of null geodesics. A vector conservation law for the null-string dust is derived. It is also demonstrated that, with proper normalization of the null-string bivector, the bivector form of the equations of motion for the timelike string also holds for the null string.