2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/189394The recently developed gauge-invariant formalism for the treatment of fluctuations in holographic renormalization group (RG) flows overcomes most of the previously encountered technical difficulties. I summarize the formalism and present its application to the GPPZ flow, where scattering amplitudes between glueball states have been calculated and a set of selection rules been found.talk given at the RTN workshop "The quantum structure of space-time and the geometric nature of fundamental interactions", Kolymbari, September 5-10, 2004High Energy Physics - Theorytext