COLLECTIVE EFFECTS IN BOSONIC STRINGS

Collective effects are investigated in the covariant field theories for open and closed bosonic strings. The tachyon destabilizes the perturbative vacuum and interactions induce the formation of a condensate in a new stable vacuum. The spectrum of states is considerably different from the perturbative spectrum. In particular, there are neither massless gauge bosons nor a massless graviton. Other topics such as vacuum structure, the possibility of Lorentz symmetry breaking, and the running at tree level of the coupling constant are discussed.