TYPE-B -O BOSONIC STRING SIGMA-MODELS

We provide world-sheet non-supersymmetrical actions that describe the coupling of a bosonic string to the tachyon and massless states of bot h the type-B and type-O theories. The type-B theory is derived as a tr uncation and chiral doubling of the Ramond-Ramond sector in our previo us model that connected the (1,0) heterotic string to a 10D, type-IIB supergravity background. The type-O theory then follows from a ''fermi onization'' of the type-B theory. (C) 1997 Published by Elsevier Scien ce B.V.