U(1)′ dark matter

We consider models with a gauged U(1)′, to which is coupled a fermionic standard-model singlet $\psi$. If $\psi \text{'}\mathrm{s}$ close the Universe, a Lee-Weinberg calculation gives the four-fermion coupling $G^{\prime }$ from the mass $m_{\psi }$. We can then calculate the germanium scattering cross section as a function of $m_{\psi }$. The results are nearly model independent and close to experimental limits for $10 \mathrm{GeV}\le m_{\psi }\le 100 \mathrm{GeV}$. In the region $400 \mathrm{GeV}\le m_{\psi }\le 40 \mathrm{TeV}$ the scattering cross section depends on $M_{Z^{\prime }}$, and again approaches experimental limits if $M_{Z^{\prime }}\le 2$ TeV.