Dark Matter Detectors as Dark Photon Helioscopes

TL;DR

The paper investigates dark photons mixing kinetically with the SM photon via $\kappa$, with mass $m_V$ from either the Stueckelberg (SC) or Higgsing (HC) mechanisms. It computes the solar production spectra for both cases and the subsequent absorption rates in low-threshold detectors by linking to the medium's dielectric function, then confronts these predictions with XENON10 data to set the strongest direct constraints to date, notably $\kappa m_V<3\times10^{-12}\ \mathrm{eV}$ for small $m_V$ in the SC scenario and competitive bounds for Higgsed (mini-charged) cases. The approach demonstrates that dark matter detectors with low energy thresholds can function as highly sensitive helioscopes for dark photons, surpassing astrophysical limits over a wide $m_V$ range and potentially constraining other light exotica. The results emphasize the rapid payoff from existing and forthcoming low-threshold experiments for probing new light vector sectors coupled through a hypercharge-like portal.

Abstract

Light new particles with masses below 10 keV, often considered as a plausible extension of the Standard Model, will be emitted from the solar interior, and can be detected on the Earth with a variety of experimental tools. Here we analyze the new "dark" vector state V, a massive vector boson mixed with the photon via an angle kappa, that in the limit of the small mass m_V has its emission spectrum strongly peaked at low energies. Thus, we utilize the constraints on the atomic ionization rate imposed by the results of the XENON10 experiment to set the limit on the parameters of this model: kappa times m_V< 3 times10^{-12} eV. This makes low-threshold Dark Matter experiments the most sensitive dark vector helioscopes, as our result not only improves current experimental bounds from other searches by several orders of magnitude, but also surpasses even the most stringent astrophysical and cosmological limits in a seven-decade-wide interval of m_V. We generalize this approach to other light exotic particles, and set the most stringent direct constraints on "mini-charged" particles.

Figures (2)

• Figure 1: Fluxes at the Earth as functions of energy for both the SC and HC dark photon for $\kappa = 10^{-12}$. The red and black thick dashed curves show the contribution from longitudinal dark radiation (DR) for $m_V=$1 eV and 100 eV, respectively. The corresponding thin curves show the transverse contribution. The blue and purple dotted dashed curves show the contribution from the Higgs-strahlung (HS) process for $e'=1$ and 0.01, respectively.
• Figure 2: Constraints on $\kappa$ as functions of $m_V$. The solid, dashed, dot-dashed and dotted curves show constraints from the energy loss of the Sun by requiring that the dark photon luminosty does not exceed 10% of the standard solar luminosity Gondolo:2008dd, energy loss in horizontal branch (HB) stars, the XENON10 experiment and the CoGeNT experiment, respectively. The thick curves are for the SC, whereas the thin curves are for the HC with $e'=0.1$. For comparison, the current bound (gray shading) from the LSW-type experiments are shown (see Ref. Ehret:2010mh for details). The conservative constraint from the CAST experiment Andriamonje:2007ew by considering the contributions from only the transverse modes Redondo:2008aa is also shown in green shading.The orange shaded region is excluded from tests of the inverse square law of the Coulomb interaction Bartlett:1988yy.