Tachyon stabilization in the AdS/CFT correspondence

We consider duality between type OB string theory on AdS(5) x S-5 and the p lanar CFT on N electric D3-branes coincident with N magnetic D3-branes. It has been argued that this theory is stable up to a critical value of the 't Hooft coupling but is unstable beyond that point. We suggest that from the gauge theory point of view the development of instability is associated wi th singularity in the dimension of the operator corresponding to the tachyo n field via the AdS/CFT map. Such singularities are common in large N theor ies because summation over planar graphs typically has a finite radius of c onvergence. Hence we expect transitions between stability and instability f or string theories in AdS backgrounds that are dual to certain large N gaug e theories: if there are tachyons for large AdS radius then they may be sta bilized by reducing the radius below a critical value of order the string s cale. (C) 1999 Elsevier Science B.V. All rights reserved.