Probing P- and CP-violation in dark matter interactions

Discrete symmetries played a central role in elucidating the structure of the weak interactions, and they will probably be equally crucial regarding the interactions of the dark matter (DM) particle - whose nature remains elusive. In this work we show that signals in future direct detection experiments can be used to test, in a model-independent way, for P- and CP-violation in DM-nucleus interactions. The analysis is performed within the most general effective theory for non-relativistic spin-0 DM-nucleus interactions mediated by the exchange of a heavy particle. Assuming an idealised xenon detector, we calculate the expected number of DM signal events required to reject P and CP invariant dark matternucleus interactions. For a DM mass of 30 GeV (or higher), this number lies between about 10 and 300 DM signal events, depending on how P and CP invariance are modeled. Future direct detection experiments, therefore, have the potential to reveal P- and CP-violation in DM interactions, making a decisive step toward the identification of the DM particle.