  Essential properties of halo nuclei can be described in terms of a few
low-energy constants. For neutron halo nuclei, analytical results can be found
for wave functions and electromagnetic transition matrix-elements in simple but
well-adapted models. These wave functions can be used to study nuclear
reactions; an especially simple and instructive example is Coulomb excitation.
A systematic expansion in terms of small parameters can be given. We present
scaling laws for excitation amplitudes and cross sections. The results can be
used to analyze experiments like ${}^{11}$Be Coulomb excitation. They also
serve as benchmark tests for more involved reaction theories.
