Softly shifting away from dark matter direct detection

We propose a soft-breaking mechanism for dark matter (DM) shift symmetry in a class of composite dark matter models, where both DM and the Higgs boson arise as pseudo Nambu-Goldstone bosons from novel strong dynamics. Our mechanism is utilized to suppress the nonderivative portal coupling between the Higgs boson and DM particle, which can evade the stringent bound of current DM direct detection experiments. Otherwise, this nonderivative portal coupling would naturally be at the same order of the Higgs quartic, rendering this class of models under severe crisis. For realizing the soft-breaking mechanism, we introduce vectorlike top partners dubbed softons to restore the shift symmetry of DM in the top Yukawa sector, which, however, is only broken by the softon masses. The portal coupling automatically vanishes as the shift-symmetry-breaking softon masses approach zero. Specifically, we present a proof-of-concept model of soft breaking based on the coset O6)/O(5) and the simplest fermion embedding, and study its DM phenomenology, where we show a large amount of novel parameter space is opened up by using the soft-breaking mechanism.

Automated summary

We propose a soft-breaking mechanism for dark matter (DM) shift symmetry in a class of composite dark matter models, which is utilized to suppress the nonderivative portal coupling between the Higgs boson and DM particle. By introducing softons, the shift symmetry of DM in the top Yukawa sector is restored, leading to a large amount of novel parameter space being opened up.