Scale-invariant processes, and hereafter processes with broken versions of this symmetry, are studied by means of the Lamperti transformation, a one-toone transformation linking stationary and self-similar processes. A general overview of the use of the transformation, and of the stationary generators it builds, is given for modelling and analysis of scale invariance. We put an emphasis on generalizations to non-strictly scale-invariant situations. The examples of discrete scale invariance and finite-size scale invariance are developed by means of the Lamperti transformation framework, and some specific examples of processes with these generalized symmetries are given.
Scale invariance and beyondScale invariance, once acknowledged as an important feature [39], has often been used as a fundamental property to handle physical phenomena. The idea that some quantity behaves the same at each scale, irrelevant to the scale at which it is observed, has made its way into the study of geometrical fractal sets [21], 1/f spectra, long memory [6], simple dimensional analysis [5] or involved analysis of critical systems in statistical physics [22], textures in geophysics [52] or image processing [38], turbulence of fluids [27], data of network traffic [45] and so on.Common as this invariance may be in physics, it often eludes general and convenient methods or models. Even though there is no single definition of scale invariance [19], it is often described as a symmetry of the system relatively to a transformation of scale, that is