Fractional D-branes and their gauge duals

We study the classical geometry associated to fractional D3-branes of type- IIB string theory on R-4/Z(2) which provide the gravitational dual for N = 2 super Yang-Mills theory in four dimensions. As one can expect from the la ck of conformal invariance on the gauge theory side, the gravitational back ground displays a repulson-like singularity. It turns out however, that suc h singularity can be excised by an enhancon mechanism. The complete knowled ge of the classical supergravity solution allows us to identify the couplin g constant of the dual gauge theory in terms of the string parameters and t o find a logarithmic running that is governed precisely by the beta functio n of the N = 2 super Yang-Mills theory.