Membranes and Other Extendons (p-branes)

The physics of relativistic extended objects, or `extendons', as the authors term them, is a rapidly evolving sector of `hard' theoretical physics. One of the most intriguing aspects of this speculative field of research is to range over vastly different domains of physics, bridging the gap between micro and macro-cosmology. As a meaningful example, let us recall the almost ubiquitous role of strings in modern physics, since their first appearance in hadronic physics. Today, they are supposed to be the fundamental building blocks of the spacetime fabric itself. But linelike objects are also met as topological defects in superconductor physics, or as cosmic strings in cosmology. Moreover, it has been recently suggested that some basic mechanisms, ruling biological systems, can be formally described in terms of string and membrane dynamics as well.