Softly shifting away from dark matter direct detection

TL;DR

This paper introduces a soft breaking mechanism in composite dark matter models to suppress Higgs-DM interactions, allowing models to evade direct detection bounds and opening new parameter space.

Contribution

It presents a novel soft breaking mechanism using vector-like top partners to naturally suppress the Higgs-DM portal coupling in composite models.

Findings

Suppression of non-derivative portal coupling evades direct detection bounds.

Introduction of softons restores shift symmetry, controlling portal coupling.

New viable parameter space for composite dark matter models.

Abstract

We propose 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 non-derivative portal coupling between the Higgs boson and DM particle, which can evade the stringent bound of current DM direct detection experiments. Otherwise this non-derivative portal coupling would naturally be at the same order of the Higgs quartic, rendering this class of models under severe crisis. For realizing soft breaking mechanism, we introduce vector-like top partners, dubbed as "softons", to restore the shift symmetry of DM in top Yukawa sector, which however is only broken by the softon masses. The portal coupling would automatically vanish as the shift-symmetry-breaking softon masses approach zero. Specifically we present a proof-of-concept model of soft breaking, based on the coset $O(6)/O(5)$ 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.