  The Standard Model of particle physics has been remarkably successful in
describing present experimental results. However, it is assumed to be only a
low-energy effective theory which will break down at higher energy scales,
theoretically motivated to be around 1 TeV. There are a variety of proposed
models of new physics beyond the Standard Model, most notably supersymmetric
and extra dimension models. New charged and neutral heavy leptons are a feature
of a number of theories of new physics, including the `intermediate scale'
class of supersymmetric models. Using a time-of-flight technique to detect the
charged leptons at the Large Hadron Collider, the discovery range (in the
particular scenario studied in the first part of this thesis) is found to
extend up to masses of 950 GeV. Extra dimension models, particularly those with
large extra dimensions, allow the possible experimental production of black
holes. The remainder of the thesis describes some theoretical results and
computational tools necessary to model the production and decay of these
miniature black holes at future particle colliders. The grey-body factors which
describe the Hawking radiation emitted by higher-dimensional black holes are
calculated numerically for the first time and then incorporated in a Monte
Carlo black hole event generator; this can be used to model black hole
production and decay at next-generation colliders. It is hoped that this
generator will allow more detailed examination of black hole signatures and
help to devise a method for extracting the number of extra dimensions present
in nature.
