CHIRAL GAUGED WZNW MODELS AND HETEROTIC STRING BACKGROUNDS

We construct new heterotic string backgrounds which are analogous to s uperstring solutions corresponding to coset models but are not simply the ''embeddings'' of the latter. They are described by the (1,0) supe rsymmetric extension of the G/H chiral gauged WZNW models. The ''chira l gauged'' WZNW action differs from the standard gauged WZNW action by the absence of the AABAR-term (and thus is not gauge invariant in the usual sense) but can still be expressed as a combination of WZNW acti ons and is conformally invariant. We explain a close relation between gauged and chiral gauged WZNW models and prove that in the case of the abelian H the G/H chiral gauged theory is equivalent to a particular (G x H)/H gauged WZNW theory. In contrast to the gauged WZNW model, th e chiral gauged one admits a (1,0) supersymmetric extension which is c onsistent at the quantum level. Integrating out the 2d gauge field we determine the exact (in alpha') form of the couplings of the correspon ding heterotic sigma model. While in the bosonic (superstring) cases a ll the fields depend (do not depend) nontrivially on alpha' here the m etric receives only one O(alpha') correction while the antisymmetric t ensor and the dilaton remain semiclassical. As a simplest example, we discuss the basic D = 3 solution which is the heterotic string counter part of the ''black string'' SL(2, R) x R/R background.