Abstract
Direct detection of light dark matter (DM), below the GeV scale, through electron recoil can be efficient if DM has a velocity well above the virial value of $v\sim 10^{-3}$. We point out that if there is a long range attractive force sourced by bulk ordinary matter, i.e. baryons or electrons, DM can be accelerated towards the Earth and reach velocities $v\sim 0.1$ near the Earth's surface. In this "attractive scenario," all DM will be boosted to high velocities by the time it reaches direct detection apparatuses in laboratories. Furthermore, the attractive force leads to an enhanced DM number density at the Earth facilitating DM detection even more. We elucidate the implications of this scenario for electron recoil direct detection experiments and find parameters that could lead to potential signals, while being consistent with stellar cooling and other bounds. Our scenario can potentially explain the recent excess in electron recoil signals reported by the XENON1T experiment in the $\sim$ keV energy regime as well as the hint for non-standard stellar cooling.
Highlights
A variety of astronomical and cosmological observations have established that the Universe contains a substance of little, if any, interaction with ordinary matter made of atoms
Given the diversity of particles and forces that constitute the “visible” sector encoded in the Standard Model (SM) of particle physics, it is reasonable to consider whether dark matter (DM) resides within a “dark sector” that comprises a number of new states and forces that only feebly interact with the SM
The questions surrounding the physics underlying electroweak symmetry breaking in the SM and its extensions led to an early focus to look for DM around the weak scale ∼100 GeV
Summary
A variety of astronomical and cosmological observations have established that the Universe contains a substance of little, if any, interaction with ordinary matter made of atoms. Direct detection of light DM, below the GeV scale, motivates looking for electron recoil signals. Detection of a signal in electron recoil in an experiment with ≳keV energy threshold requires velocities near v ∼ 0.1, which is well above the escape velocity. To look for typical DM in the sub-GeV regime, one needs to devise experimental techniques with detection thresholds ≪ keV [2,3,4,5,6] (for novel ideas see [7,8,9,10]). As will be discussed in the following, our scenario opens up a new possibility for detection of light DM at existing and planned experiments that use electron recoil with thresholds of ∼keV. We will introduce an example of a short range interaction that will be necessary for detectable scatterings of DM on electrons
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