Direct detection of dark energy: the XENON1T excess and future prospects
  We explore the prospects for direct detection of dark energy by current and
upcoming terrestrial dark matter direct detection experiments. If dark energy
is driven by a new light degree of freedom coupled to matter and photons then
dark energy quanta are predicted to be produced in the Sun. These quanta
free-stream towards Earth where they can interact with Standard Model particles
in the detection chambers of direct detection experiments, presenting the
possibility that these experiments could be used to test dark energy. Screening
mechanisms, which suppress fifth forces associated with new light particles,
and are a necessary feature of many dark energy models, prevent production
processes from occurring in the core of the Sun, and similarly, in the cores of
red giant, horizontal branch, and white dwarf stars. Instead, the coupling of
dark energy to photons leads to production in the strong magnetic field of the
solar tachocline via a mechanism analogous to the Primakoff process. This then
allows for detectable signals on Earth while evading the strong constraints
that would typically result from stellar probes of new light particles. As an
example, we examine whether the electron recoil excess recently reported by the
XENON1T collaboration can be explained by chameleon-screened dark energy, and
find that such a model is preferred over the background-only hypothesis at the
$2.0\sigma$ level, in a large range of parameter space not excluded by stellar
(or other) probes. This raises the tantalizing possibility that XENON1T may
have achieved the first direct detection of dark energy. Finally, we study the
prospects for confirming this scenario using planned future detectors such as
XENONnT, PandaX-4T, and LUX-ZEPLIN.
