The hemispherical asymmetry from a scale-dependent inflationary
  bispectrum
  If the primordial bispectrum is sufficiently large then the CMB hemispherical
asymmetry may be explained by a large-scale mode of exceptional amplitude which
perturbs the zeta two-point function. We extend previous calculations, which
were restricted to one- or two-source scenarios, by providing a method to
compute the response of the two-point function in any model yielding a
'local-like' bispectrum. In general, this shows that it is not the reduced
bispectrum fNL which sources the amplitude and scale-dependence of the mode
coupling but rather a combination of 'response functions'. We discuss why it is
difficult to construct successful scenarios and enumerate the fine-tunings
which seem to be required. Finally, we exhibit a concrete model which can be
contrived to match the observational constraints and show that to a Planck-like
experiment it would appear to have |fNL-local| ~ |fNL-equi| ~ |fNL-ortho| ~ 1.
Therefore, contrary to previous analyses, we conclude that it is possible to
generate the asymmetry while respecting observational constraints on the
bispectrum and low-ell multipoles even without tuning our location on the
long-wavelength mode.
