Effective scalar four-fermion interaction for Ge-phobic exothermic dark
  matter and the CDMS-II Silicon excess
  We discuss within the framework of effective four-fermion scalar interaction
the phenomenology of a Weakly Interacting Massive Particle (WIMP) Dirac Dark
Matter candidate which is exothermic (i.e. is metastable and interacts with
nuclear targets down-scattering to a lower-mass state) and $Ge$-phobic (i.e.
whose couplings to quarks violate isospin symmetry leading to a suppression of
its cross section off Germanium targets). We discuss the specific example of
the CDMS-II Silicon three-candidate effect showing that a region of the
parameter space of the model exists where WIMP scatterings can explain the
excess in compliance with other experimental constraints, while at the same
time the Dark Matter particle can have a thermal relic density compatible with
observation. In this scenario the metastable state $\chi$ and the lowest-mass
one $\chi^{\prime}$ have approximately the same density in the present Universe
and in our Galaxy, but direct detection experiments are only sensitive to the
down-scatters of $\chi$ to $\chi^{\prime}$. We include a discussion of the
recently calculated Next-to-Leading Order corrections to Dark Matter-nucleus
scattering, showing that their impact on the phenomenology is typically small,
but can become sizable in the same parameter space where the thermal relic
density is compatible to observation.
