ABSTRACT
This chapter discusses the physical motivation for renormalisation of parameters in classical field theory. In the discussion, the Lagrangian is given in terms of the ‘bare’ or ‘unrenormalised’ quantities. The objective of renormalisation is to calculate cross sections, and other observable quantities, as functions of the renormalised quantities. The chapter discusses the evaluation of Feynman integrals and shows how renormalisation, which is necessary in any interacting field theory, enables to remove the infinites by absorbing them into the renormalisation constants. The precise way in which the parameters of the counter term Lagrangian are fixed is called a ‘renormalisation scheme’. The simplest such scheme, which is also particularly suited to gauge theories, is one which emerges naturally from the dimensional regularisation.
