EFT interpretation of XENON1T electron recoil excess: Neutrinos and dark matter

We scrutinize the XENON1T electron recoil excess in the scalar-singlet-extended dark matter effective field theory. We confront it with various astrophysical and laboratory constraints both in a general setup and in the more specific, recently proposed, variant with leptophilic $Z_2$-odd mediators. The latter also provide mass to the light leptons via suppressed $Z_2$ breaking, a structure that is well fitting with the nature of the observed excess and the discrete symmetry leads to nonstandard dark-matter interactions. We find that the excess can be explained by neutrino–electron interactions, linked with the neutrino and electron masses, while dark-matter–electron scattering does not lead to statistically significant improvement. We analyze the parameter space preferred by the anomaly and find severe constraints that can only be avoided in certain corners of parameter space. Potentially problematic bounds on electron couplings from big-bang nucleosynthesis can be circumvented via a late phase transition in the new scalar sector.

Figure 1

Comparison between an exemplary differential event rate for a scalar with $m_s=60\mathrm{eV}$ and $\sqrt{y_e^s{y}_{\nu }^s}=7.9\times {10}^{-7}$ and the data as reported by [1]. The full differential event rate is shown in blue while the pure signal (background) contribution is depicted in orange (red).

Figure 2

Comparison between the best fit differential event rate for a DM particle with $m_{\chi }=10\mathrm{GeV}$ and ${\sigma }_{e\chi }=1.25\times {10}^{-39}{\mathrm{cm}}^2$ and the data. The style is similar to Fig. 1 and for better visibility we also show the signal rate enhanced by a factor of 5 as an orange dashed line.

Figure 3

Isocontours of correct DM relic density assuming production through freeze-in and considering the assignations of model parameters for BM1 (red) and BM2 (black). The reheating temperature $T_R$ has been set to 100 GeV.

Figure 4

Constraints in the $m_{S/s}–y_e^{S/s}$-plane from [50] and our own analysis, including our two BM points. For a discussion of the various limits and their shading see the main text.

Figure 5

Constraints in the $m_s–y_{\nu }^s$-plane including our two BM points. Note that the heavier mediator has too small couplings to appear.

Figure 6

Constraints in the $y_e^s–y_{\nu }^s$-plane for a 60 eV mediator (as in BM2) and the $1\sigma$ preferred region from our fit to the XENON1T excess. The BBN bound on the electron coupling, indicated by the hatched region, can be circumvent by a late time phase transition.

Figure 7

Constraints in the $y_e^s–y_{\nu }^s$-plane for a 20 keV mediator (as in BM1) and the $1\sigma$ preferred region from our fit to the XENON1T excess. The BBN bound on the electron coupling, indicated by the hatched region, can be circumvent by a late time phase transition.