  We propose a new model for the hemispherical power asymmetry of the CMB based
on modulated reheating. Non-Gaussianity from modulated reheating can be small
enough to satisfy the bound from Planck if the dominant modulation of the
inflaton decay rate is linear in the modulating field $\sigma$. $\sigma$ must
then acquire a spatially-modulated power spectrum with a red scale-dependence.
This can be achieved if the primordial perturbation of $\sigma$ is generated
via tachyonic growth of a complex scalar field. Modulated reheating due to
$\sigma$ then produces a spatially modulated and scale-dependent sub-dominant
contribution to the adiabatic density perturbation. We show that it is possible
to account for the observed asymmetry while remaining consistent with bounds
from quasar number counts, non-Gaussianity and the CMB temperature quadupole.
The model predicts that the adiabatic perturbation spectral index and its
running will be modified by the modulated reheating component.
