  In this paper we develop a formalism to analyze the spectrum of small
perturbations about arbitrary solutions of Einstein, Yang-Mills and scalar
systems. We consider a general system of gravitational, gauge and scalar fields
in a $D-$dimensional space-time and give the bilinear action for the
fluctuations of the fields in the system around an arbitrary solution of the
classical field equations. We then consider warped geometries, popular in brane
world scenarios, and use the light cone gauge to separate the bilinear action
into a totally decoupled spin-two, -one and -zero fluctuations. We apply our
general scheme to several examples and discuss in particular localization of
abelian and non-abelian gauge fields of the standard model to branes generated
by scalar fields. We show in particular that the Nielsen-Olsen string solution
gives rise to a normalizable localized spin-1 field in any number of
dimensions.
