Modelling Giant Radio Halos
  We review models for giant radio halos in clusters of galaxies, with a focus
on numerical and theoretical work. After summarising the most important
observations of these objects, we present an introduction to the theoretical
aspects of hadronic models. We compare these models with observations using
simulations and find severe problems for hadronic models. We give a short
introduction to reacceleration models and show results from the first
simulation of CRe reaccel- eration in cluster mergers. We find that in-line
with previous theoretical work, reacceleration models are able to elegantly
explain main observables of giant radio halos.
