Kasper Risager Larsen

Title: Unitarity and On-Shell Recursion Methods for Scattering Amplitudes

Submitted for the degree of Ph.D. in Physics from the Niels Bohr Institute, Faculty of Science,
University of Copenhagen.
November 2007

Academic advisor:
Poul Henrik Damgaard

Abstract

Unitarity and On-Shell Recursion Methods for Scattering Amplitudes

This thesis describes some of the recent (and some less recent) developments in calculational techniques for scattering amplitudes in quantum field theory.

The focus is on on-shell recursion relations in complex momenta and on the use of unitarity methods for loop calculations. In particular, on-shell recursion is related to the MHV rules for computing tree-level gauge amplitudes and used to extend the MHV rules to graviton scattering.

Combinations of unitarity cut techniques and recursion is used to argue for the “No-Triangle Hypothesis” in N = 8 supergravity which is related to its UV behaviour.

Finally, combinations of unitarity and recursion is used to demonstrate the full calculation of a oneloop amplitude involving a Higgs particle and four gluons in the limit of large top mass.