  We derive scaling relations for the extension statistics and the confinement
free energy for a semi-flexible polymer confined to a channel with a
rectangular cross-section. Our motivation are recent numerical results [Gupta
{\em et al.}, JCP {\bf 140} (2014) 214901] indicating that extensional
fluctuations are quite different in rectangular channels compared to square
channels. Our results are of direct relevance for interpreting current
experiments on DNA molecules confined to nano-channels, as many experiments are
performed for rectangular channels with large aspect ratios while theoretical
and simulation results are usually obtained for square channels.

Soft Condensed Matter