  Cosmic microwave background lensing has become a new cosmological probe,
carrying rich information on the matter power spectrum and distances over the
redshift range $z\approx1$-4. We investigate the role of scale dependent new
physics, such as from modified gravity, neutrino mass, and cold (low sound
speed) dark energy, and its signature on CMB lensing. The distinction between
different scale dependences, and the different redshift dependent weighting of
the matter power spectrum entering into CMB lensing and other power spectra,
imply that CMB lensing can probe simultaneously a diverse range of physics. We
highlight the role of arcminute resolution polarization experiments for
distinguishing between physical effects.
