Tachyon splits the (d=2 string) black-hole horizon and turns it singular.

Abstract

We present a static solution for d=2 critical string theory including the tachyon T but not its potential V(T). This solution thus incorporates tachyon back reaction and, when T=0, reduces to the black hole solution. When T\ensuremath{\ne}0 one finds that (1) the Schwarzschild horizon of the above black hole splits into two, resembling Reissner-Nordstrom horizons and (2) the curvature scalar develops new singularities at the horizons. These features, as we argue, will persist even with V(T) present. Some possible methods for removing these singularities are discussed.