Description
The problem of infrared divergences in gauge-theory scattering amplitudes
is as old as quantum field theory, and has been `solved’ many times, with increasing
degrees of sophistication. Perhaps surprisingly, it is still at the forefront of current
research, both in view of theoretical developments, and for phenomenological
applications. I will provide an overview of the state of the art for infrared factorisation
of scattering amplitudes, and then I will briefly present two current research directions:
the problem of infrared subtraction for the precision calculation of collider observables,
and the surprising connection between infrared behaviour in d=4 and two-dimensional
conformal field theories on the `celestial sphere’.