I review how methods from mesoscopic physics can be applied to describe the
multiple wave scattering and complex wave dynamics in non-hermitian
PT-symmetric resonators, where an absorbing region is coupled symmetrically to
an amplifying region. Scattering theory serves as a convenient tool to classify
the symmetries beyond the single-channel case and leads to effective
descriptions which can be formulated in the energy domain (via Hamiltonians)
and in the time domain (via time evolution operators). These models can then be
used to identify the mesoscopic time and energy scales which govern the
spectral transition from real to complex eigenvalues. The possible presence of
magneto-optical effects (a finite vector potential) in multichannel systems
leads to a variant (termed PTT' symmetry) which imposes the same spectral
constraints as PT symmetry. I also provide multichannel versions of generalized
flux-conservation laws.Comment: 10 pages, 5 figures, minireview for a theme issue, Philosophical
Transactions of the Royal Society
