  In quantum field theories with massless particles, states carrying a
nontrivial superselection charge may have very poor localisation properties
when compared to the vacuum. In this case, replacing the vacuum with a suitable
``infravacuum'' state can improve the localisability of the charges in such a
way that the Doplicher-Haag-Roberts (DHR) theory of superselection sectors is
applicable.
  As an explicit example for this phenomenon, we consider a certain class of
sectors of the free massless scalar field. These sectors carry a charge of
electric type, and the corresponding infravacuum background may be interpreted
as a cloud of infrared radiation.
  Motivated by this situation, we propose a model-independent definition of
infravacuum representations and derive some of their properties. We analyse in
particular their role as reference representations for DHR theory and
investigate to what an extent the absence of a translation invariant vector
affects the results of the DHR analysis. Special emphasis is put on the
functorial aspects of the theory and on the description of the covariance and
the spectral properties of charged sectors in terms of so-called charge
transporting cocycles.
