Abstract
The XENON1T collaboration reported an excess of the low-energy electron recoil events between 1 and 7 keV. We explore the possibility to explain such an anomaly by the MeV-scale dark matter (DM) heated by the interior of the Sun due to the same DM-electron interaction as in the detector. The kinetic energies of heated DM particles can reach a few keV, and can potentially account for the excess signals detected by XENON1T. We study different form factors of the DM-electron interactions, F(q) ∝ qi with q being the momentum exchange and i = 0, 1, 2, and find that for all these cases the inclusion of the Sun-heated DM component improves the fit to the XENON1T data. The inferred DM-electron scattering cross section (at q = αme where α is the fine structure constant and me is electron mass) is from ∼ 10−38 cm2 (for i = 0) to ∼ 10−42 cm2 (for i = 2). We also derive constraints on the DM-electron cross sections for these form factors, which are stronger than previous results with similar assumptions. We emphasize that the Sun-heated DM scenario relies on the minimum assumption on DM models, which serves as a general explanation of the XENON1T anomaly via DM-electron interaction. The spectrum of the Sun-heated DM is typically soft comparing to other boosted DM, so the small recoil events are expected to be abundant in this scenario. More sensitive direct detection experiments with lower thresholds can possibly distinguish this scenario with other boosted DM models or solar axion models.
Highlights
The XENON1T collaboration reported an excess of the low-energy electron recoil events between 1 and 7 keV
We study different form factors of the dark matter (DM)-electron interactions, F (q) ∝ qi with q being the momentum exchange and i = 0, 1, 2, and find that for all these cases the inclusion of the Sun-heated DM component improves the fit to the XENON1T data
We emphasize that the Sun-heated DM scenario relies on the minimum assumption on DM models, which serves as a general explanation of the XENON1T anomaly via DM-electron interaction
Summary
Where Φhalo is the DM flux in the local Milky Way halo, Rcore ∼ 0.2R is the core radius of the Sun, d ≡ 1.5×1013 cm is the Sun-Earth distance, Sg describes the gravitational focusing effect which enhances the scatterings, Rscatt is the characteristic scattering radius at which the DM-electron scattering once on average, λ is the mean free path of a DM particle inside the core of the Sun. We consider three examples of form factors: F = 1, F These operators all originate from a heavy mediator whose mass is much heavier than the typical momentum transfer. The latter two q-dependent form factors can be derived, for example, from dimension six operators with scalar-pseudoscalar interaction χγ5χee and pseudoscalar-pseudoscalar interaction χγ5χeγ5e, respectively [24]. Where F (Edm) is the normalized kinetic energy distribution of DM with the reflection of the Sun, and 16πR2 is the impact area adopted in the simulation. The energy spectrum of the heated DM depends on the DM mass and the scattering cross section [23].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
