2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/210374We present for the first time the complete matter power spectrum for $R^n$ gravity which has been derived from the fourth order scalar perturbation equations. This leads to the discovery of a characteristic signature of fourth order gravity in the matter power spectrum, the details of which have not seen before in other studies in this area and therefore provides a crucial test for fourth order gravity on cosmological scales.4 pages and 3 figuresAstrophysicsGeneral Relativity and Quantum Cosmologytext