Triple pomeron vertex in the limit N_c\rightarrow\infty

In the hard pomeron theory with the number of colours the diffractive amplitude obtained in 3] is compared with the results found for in 1] and in the dipole approach in 5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in 1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling. Received: 11 December 1997 / Revised version: 6 February 1998 / Published online: 7 August 1998