D-branes and dual gauge theories in type 0 strings

We consider the type 0 theories, obtained from the closed NSR string by a d iagonal GSO projection which excludes space-time fermions, and study the D- branes in these theories. The low-energy dynamics of N coincident D-branes is governed by a U(N) gauge theory coupled to adjoint scalar fields, It is tempting to look for the type 0 string duals of such bosonic gauge theories in the background of the R-R charged p-brane classical solutions. This res ults in a picture analogous to the one recently proposed by Polyakov (hep-t h/9809057). One of the serious problems that needs to be resolved is the cl osed string tachyon mode which couples to the D-branes and appears to cause an instability. We study the tachyon terms in the type 0 effective action and argue that the background R-R Aux provides a positive shift of the (mas s)(2) of the tachyon. Thus, for sufficiently large flux, the tachyonic inst ability may be cured, removing the most basic obstacle to constructing the type 0 duals of non-supersymmetric gauge theories. We further find that the tachyon acquires an expectation value in the presence of the R-R flux. Thi s effect is crucial for breaking the conformal invariance in the dual descr iption of the 3 + 1-dimensional non-supersymmetric gauge theory. (C) 1999 E lsevier Science B.V.