Perturbations of SNe Ia lightcurves, colors and spectral features by
  circumstellar dust
  It has been suggested that multiple scattering on circumstellar dust could
explain the non-standard reddening observed in the line-of-sight to Type Ia
supernovae. In this work we use Monte Carlo simulations to examine how the
scattered light would affect the shape of optical lightcurves and spectral
features. We find that the effects on the lightcurve widths, apparent time
evolution of color excess and blending of spectral features originating at
different photospheric velocities should allow for tests of the circumstellar
dust hypothesis on a case by case basis. Our simulations also show that for
circumstellar shells with radii r=1e16-1e19 cm, the lightcurve modifications
are well described by the empirical Dm_15 parameter and intrinsic color
variations of order sigma_{BV}=0.05-0.1 arise naturally. For large shell radii
an excess lightcurve tail is expected in B-band, as observed in e.g. SN2006X.
