  The diffusion coefficients of heavy quarks from the coherent color
electromagnetic fields which are generated in the early stage of relativistic
heavy-ion collisions are calculated at midrapidity, and compared with those
obtained from collisions within a thermalized quark-gluon plasma. The coherent
color fields are modeled such that they are initially longitudinal and then
become isotropic. We found that the diffusion coefficients from the coherent
color fields are larger than those from collisions except for very fast heavy
quarks, and the color fields are less effective for heavy-quark energy loss.
The importance of coherent color fields for heavy-quark diffusion decreases as
energy density decreases.
