Abstract
We consider liquid xenon dark matter detectors for searching a light scalar particle produced in the solar core, specifically one that couples to electrons. Through its interaction with the electrons, the scalar particle can be produced in the Sun, mainly through Bremsstrahlung process, and subsequently it is absorbed by liquid xenon atoms, leaving prompt scintillation light and ionization events. Using the latest experimental results of XENON1T and Large Underground Xenon, we place bounds on the coupling between electrons and a light scalar as $g_{\phi ee} < 7 \times 10^{-15}$ from S1-only analysis, and as $g_{\phi ee} < 2 \times 10^{-15}$ from S2-only analysis. These can be interpreted as bounds on the mixing angle with the Higgs, $\sin \theta < 2 \times 10^{-9} \, \left(7 \times 10^{-10}\right)$, for the case of a relaxion that couples to the electrons via this mixing. The bounds are a factor few weaker than the strongest indirect bound inferred from stellar evolution considerations.
Highlights
Coupled light states arise in a wide variety of beyond the standard model (SM) scenarios
The two most common examples for such states are light fermions, with their masses being protected by chiral symmetries, and axionlike particles (ALPs); being pseudoNambu-Goldstone bosons, their masses are protected by shift symmetries
We present the constraints from the other searches on gφee
Summary
Coupled light states arise in a wide variety of beyond the standard model (SM) scenarios. Couplings to nucleons and photons open different channels for the scalar production in the Sun, such as ion-ion Bremsstrahlung and/or Primakoff production. We restrict our attention to the sub-keV mass range of these particles, m ≲ 1 keV, such that it can be copiously produced in the Sun. Once the light particle is produced, it escapes the Sun, as it only weakly couples to the SM particles, and eventually reaches the LXe detectors. Our goal in this paper is to use this signal in LXe detectors to probe the light scalar particle of sub-keV mass range. Similar ideas have already been proposed in the past to probe other weakly coupled light states, such as axions and ALPs [17,18,19,20,21,22], and dark photons [23,24,25], with DM direct detection experiments. We discuss the implications of our result in the context of several new physics scenarios in the same section
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