  Baryons both increase halo concentration through adiabatic contraction and
expel mass through feedback processes. However, it is not well understood how
the radiation fields prevalent during the epoch of reionization affect the
evolution of concentration in dark matter halos. We investigate how baryonic
physics during the epoch of reionization modify the structure of dark matter
halos in the Cosmic Reionization On Computers (CROC) simulations. We use two
different measures of halo concentration to quantify the effects. We compare
concentrations of halos matched between full physics simulations and
dark-matter-only simulations with identical initial conditions between $5 \leq
z \leq 9$. Baryons in full physics simulations do pull matter towards the
center, increasing the maximum circular velocity compared to dark-matter-only
simulations. However, their overall effects are much less than if all the
baryons were simply centrally concentrated indicating that heating processes
efficiently counteract cooling effects. Finally, we show that the baryonic
effects on halo concentrations at $z\approx5$ are relatively insensitive to
environmental variations of reionization history. These results are pertinent
to models of galaxy-halo connection during the epoch of reionization.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics