On the Effect of Nuclear Response Functions in Dark Matter Direct
  Detection
  We examine the effect of nuclear response functions, as laid out in
[Fitzpatrick et al, arXiv:1203.3542], on dark matter (DM) direct detection in
the context of well-motivated UV completions, including electric and magnetic
dipoles, anapole, spin-orbit, and pseudoscalar-mediated DM. Together, these
encompass five of the six nuclear responses extracted from the non-relativistic
effective theory of [Fitzpatrick et al, arXiv:1203.3542] (with the sixth
difficult to UV complete), with two of the six combinations corresponding to
standard spin-independent and -dependent responses. For constraints from
existing direct detection experiments, we find that only the COUPP constraint,
due to its heavy iodine target with large angular momentum and an unpaired
spin, and its large energy range sensitivity, is substantially modified by the
new responses compared to what would be inferred using the standard form
factors to model the energy dependence of the response. For heavy targets such
as xenon and germanium, the behavior of the new nuclear responses as recoil
energy increases can be substantially different than that of the standard
responses, but this has almost no impact on the constraints derived from
experiments such as LUX, XENON100 and CDMS since the maximum nuclear recoil
energy detected in these experiments is relatively low. We simulate mock data
for 80 and 250 GeV DM candidates utilizing the new nuclear responses to
highlight how they might affect a putative signal, and find the new responses
are most important for momentum-suppressed interactions such as the magnetic
dipole or pseudoscalar-mediated interaction when the target is relatively heavy
(such as xenon and iodine).
