First results on the scalar WIMP-pion coupling, using the XENON1T
  experiment
  We present first results on the scalar WIMP-pion coupling from 1 t$\times$yr
of exposure with the XENON1T experiment. This interaction is generated when the
WIMP couples to a virtual pion exchanged between the nucleons in a nucleus. In
contrast to most non-relativistic operators, these pion-exchange currents can
be coherently enhanced by the total number of nucleons, and therefore may
dominate in scenarios where spin-independent WIMP-nucleon interactions are
suppressed. Moreover, for natural values of the couplings, they dominate over
the spin-dependent channel due to their coherence in the nucleus. Using the
signal model of this new WIMP-pion channel, no significant excess is found,
leading to an upper limit cross section of $6.4\times10^{-46}$ cm$^2$ (90 %
confidence level) at 30 GeV/c$^2$ WIMP mass.
