CERN Accelerating science

The event rate for electron recoil as a function of recoil energy $E_R$ in keV. We have taken $\Delta m=2.5\,{\rm keV}$ and ${\bar\sigma}_e/m_{\chi_1}=1.0, 1.4, 1.8\times 10^{-43}\,{\rm cm}^2$ from bottom to top lines (purple, black and blue. The red line is the background model used by Xenon experiment \cite{xenon}.

Parameter space for relic density and XENON1T electron excess. The favored region by XENON1T electron excess is along the green line, the relic density is satisfied along the blue line. The purple region on the left plot is excluded by the BaBar limits on the visible and invisible decays of $Z'$. We have taken $v_\chi=-a_\chi=0.5$, $a_e=0$, and $m_\chi=0.3, 0.5\,{\rm GeV}$ on left and right plots, respectively, and $g_{Z'}=0.3$ on left and $v_e=10^{-3}$ on right. In the orange region, the relic density for the heavier state is Boltzmann-suppressed for $T_{\rm kd}=1\,{\rm MeV}$.

Parameter space for relic density and XENON1T electron excess. The favored region by XENON1T electron excess is along the green line, the relic density is satisfied along the blue line. The purple region on the left plot is excluded by the BaBar limits on the visible and invisible decays of $Z'$. We have taken $v_\chi=-a_\chi=0.5$, $a_e=0$, and $m_\chi=0.3, 0.5\,{\rm GeV}$ on left and right plots, respectively, and $g_{Z'}=0.3$ on left and $v_e=10^{-3}$ on right. In the orange region, the relic density for the heavier state is Boltzmann-suppressed for $T_{\rm kd}=1\,{\rm MeV}$.

Parameter space for relic density and XENON1T electron excess in microscopic models. (Left) $Z'$ portal: We have taken $v_\chi=-a_\chi=0.5$, $g_{Z'}=0.3$ and $m_\chi=0.3\,{\rm GeV}$. The color notations are the same as those in Fig.~\ref{relic}. (Right) Vector-like lepton portal: We have taken $v_\chi=-a_\chi=0.5$, $g_{Z'}=0.3$ and $m_\chi=0.3\,{\rm GeV}$. The red region is excluded by the X-ray searches and the gray region is disfavored by the electron mass. In the orange region, the relic density for the heavier state is Boltzmann-suppressed for $T_{\rm kd}=1\,{\rm MeV}$.

Parameter space for relic density and XENON1T electron excess in microscopic models. (Left) $Z'$ portal: We have taken $v_\chi=-a_\chi=0.5$, $g_{Z'}=0.3$ and $m_\chi=0.3\,{\rm GeV}$. The color notations are the same as those in Fig.~\ref{relic}. (Right) Vector-like lepton portal: We have taken $v_\chi=-a_\chi=0.5$, $g_{Z'}=0.3$ and $m_\chi=0.3\,{\rm GeV}$. The red region is excluded by the X-ray searches and the gray region is disfavored by the electron mass. In the orange region, the relic density for the heavier state is Boltzmann-suppressed for $T_{\rm kd}=1\,{\rm MeV}$.