  Coronal rain is ubiquitous in flare loops, forming shortly after the onset of
the solar flare. Rain is thought to be caused by a thermal instability, a
localized runaway cooling of material in the corona. The models that
demonstrate this require extremely long duration heating on the order of the
radiative cooling time, localized near the footpoints of the loops. In flares,
electron beams are thought to be the primary energy transport mechanism,
driving strong footpoint heating during the impulsive phase that causes
evaporation, filling and heating flare loops. Electron beams, however, do not
act for a long period of time, and even supposing that they did, their heating
would not remain localized at the footpoints. With a series of numerical
experiments, we show directly that these two issues mean that electron beams
are incapable of causing the formation of rain in flare loops. This result
suggests that either there is another mechanism acting in flare loops
responsible for rain, or that the modeling of the cooling of flare loops is
somehow deficient. To adequately describe flares, the standard model must
address this issue to account for the presence of coronal rain.
