Universal subhalo accretion in cold and warm dark matter cosmologies
  The influence of the large scale structure on host halos may be studied by
examining the angular infall pattern of subhalos. In particular, since warm and
cold dark matter cosmologies predict different abundances and internal
properties for halos at the low mass end of the mass function, it is
interesting to examine if there are differences in how these low mass halos are
accreted. The accretion events are defined as the moment a halo becomes a
substructure, namely when it crosses its host's virial radius. We quantify the
cosmic web at each point by the shear tensor and examine where, with respect to
its eigenvectors, such accretion events occur in cold ($\Lambda$CDM) and warm
(1keV sterile neutrino WDM) dark matter cosmological models. We find that the
CDM and WDM subhalos are preferentially accreted along the principal axis of
the shear tensor corresponding to the direction of weakest collapse. The
beaming strength is modulated by the host and subhalo masses and by the
redshift at which the accretion event occurs. Although strongest for the most
massive hosts and subhalos at high redshift, the preferential infall is found
to be always aligned with the axis of weakest collapse, thus we say that it has
universal nature. We compare the strength of beaming in the WDM cosmology with
the one found in the $\Lambda$CDM scenario. While the main findings remain the
same, the accretion in the WDM model for the most massive host halos appears
more beamed than in $\Lambda$CDM cosmology across all the redshifts.
