  Polarized Galactic foregrounds are one of the primary sources of systematic
error in measurements of the B-mode polarization of the Cosmic Microwave
Background (CMB). Experiments are becoming increasingly sensitive to
complexities in the foreground frequency spectra that are not captured by
standard parametric models, potentially affecting our ability to efficiently
separate out these components. Employing a suite of dust models encompassing a
variety of physical effects, we simulate observations of a future seven-band
CMB experiment to assess the impact of these complexities on parametric
component separation. We identify configurations of frequency bands that
minimize the `model errors' caused by fitting simple parametric models to more
complex `true' foreground spectra, which bias the inferred CMB signal. We find
that: (a) fits employing a simple two parameter modified blackbody (MBB) dust
model tend to produce significant bias in the recovered polarized CMB signal in
the presence of physically realistic dust foregrounds; (b) generalized MBB
models with three additional parameters reduce this bias in most cases, but
non-negligible biases can remain, and can be hard to detect; and (c) line of
sight effects, which give rise to frequency decorrelation, and the presence of
iron grains are the most problematic complexities in the dust emission for
recovering the true CMB signal. More sophisticated simulations will be needed
to demonstrate that future CMB experiments can successfully mitigate these more
physically realistic dust foregrounds.
