Tidal Stripping and Post-Merger Relaxation of Dark Matter Halos: Causes
  and Consequences of Mass Loss
  We study the properties of distinct dark matter halos (i.e., those that are
not subhalos) that have a final virial mass $M_{\mathrm{vir}}$ at $z = 0$ less
than their peak mass ($M_{\mathrm{peak}}$) in the Bolshoi-Planck cosmological
simulation. We identify two primary causes of halo mass loss: relaxation after
a major merger and tidal stripping by a massive neighbouring halo. Major
mergers initially boost $M_{\mathrm{vir}}$ and typically cause the final halo
to become more prolate and less relaxed and to have higher spin and lower NFW
concentration. As the halo relaxes, high energy material from the recent merger
gradually escapes beyond the virial radius, temporarily resulting in a net
negative accretion rate that reduces the halo mass by $5-15\%$ on average.
Halos that experience a major merger around $z = 0.4$ typically reach a minimum
mass near $z = 0$. Tidal stripping mainly occurs in dense regions, and it
causes halos to become less prolate and have lower spins and higher NFW
concentrations. Tidally stripped halos often lose a large fraction of their
peak mass ($> 20\%$) and most never recover (or even reattain a positive
accretion rate). Low mass halos can be strongly affected by both post-merger
mass loss and tidal stripping, while high mass halos are predominantly
influenced by post-merger mass loss and show few signs of significant tidal
stripping.
