Naturalness of Neutralino Dark Matter
  We investigate the level of fine-tuning of neutralino Dark Matter below 200
GeV in the low-energy phenomenological minimal supersymmetric Standard Model
taking into account the newest results from XENON100 and the Large Hadron
Collider as well as all other experimental bounds from collider physics and the
cosmological abundance. We find that current and future direct Dark Matter
searches significantly rule out a large area of the untuned parameter space,
but solutions survive which do not increase the level of fine-tuning. As
expected, the level of tuning tends to increase for lower cross-sections, but
regions of resonant neutralino annihilation still allow for a band at light
masses, where the fine-tuning stays small even below the current experimental
limits for direct detection cross-sections. For positive values of the
supersymmetric Higgs mass parameter \mu large portions of the allowed parameter
space are excluded, but there still exist untuned solutions at higher
neutralino masses which will essentially be ruled out if XENON1t does not
observe a signal.For negative \mu untuned solutions are not much constrained by
current limits of direct searches and, if the neutralino mass was found outside
the resonance regions, a negative \mu-term would be favored from a fine-tuning
perspective. Light stau annihilation plays an important role to fulfill the
relic density condition in certain neutralino mass regions. Finally we discuss,
in addition to the amount of tuning for certain regions in the neutralino
mass-direct detection cross-section plane, the parameter mapping distribution
if the allowed model parameter space is chosen to be scanned homogeneously
(randomized).
