Sun heated MeV-scale dark matter and the XENON1T electron recoil excess

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.

Global fits of axion-like particles to XENON1T and astrophysical data

“…appears to exclude the XENON1T anomaly best-fit ALP-nucleon coupling,ĝ eff aN ≈ 10 −6 , by several orders of magnitude. 6 However, the ALP-nucleon coupling only impacts the 57 Fe component of the signal, a monochromatic feature at around 14.4 keV, whereas it is the ABC and Primakoff components that could explain the XENON1T excess. Setting g eff aN = 0, we find that the minimum χ 2 value for the solar ALP case would change from χ 2 = 29.2 to 30.9, i.e., the effect of the SN1987A constraint on the solar ALPs hypothesis would be small.…”

“…One set of options is based around the existence of dark matter (DM) particles that either scatter inelastically in the detector [4,5,12,21,37,[46][47][48] or are boosted to semi-relativistic velocities via some other process before scattering elastically off electrons [10,15,17,[49][50][51][52]. A 2 keV -3 keV dark photon with a small (10 −15 ) kinetic mixing with ordinary photons [2,16,[53][54][55] or a massive dark photon produced from solar emission [6,11,54] (with the caveat of ref. [54]) may also explain the excess.…”

Solar Active-Sterile Neutrino Conversion with Atomic Effects at Dark Matter Direct Detection Experiments

“…Note that the normalization of K-factor varies in literature [66,68,71,83]. In our definition (15), the summation over m and m gives a factor of 2l + 1 and 2l + 1, respectively. That 2l + 1 factor has been canceled with the one in (14).…”

“…Since the bound and ionized states are orthogonal to each other, the product oscillates symmetrically around the vanishing value so that the integration should also vanish. The third component, the Bessel function j L (|q|r), enters the atomic form factor to render a nonzero K-factor (15). The full combination r 2 R * nl R Trl j L (|q|r) (red dashed) has asymmetric oscillation so that its integration can be nonzero.…”

“…The excess might indicate new physics beyond the SM (BSM) if not the tritium background [5]. Possible explanations include axion or axion-like particles [6][7][8][9][10][11][12][13][14], elastic [15][16][17][18][19][20][21][22][23][24][25] and inelastic [26][27][28][29][30][31][32][33][34][35][36][37] scattering between DM and electron, the Migdal effect of DM scattering with nuclei [38], and DM decay [39][40][41][42]. Another possibility is sterile neutrino as DM in our galaxy.…”