Spontaneous CP Violation and Light Particles in The Littlest Higgs

TL;DR

This paper explores how spontaneous CP violation and light particles naturally emerge in Littlest Higgs models due to the interplay of global symmetry breaking and explicit symmetry breaking, impacting phenomenology.

Contribution

It demonstrates that explicit symmetry breaking in Littlest Higgs models can induce spontaneous CP violation and light modes, providing new insights into model phenomenology and CP violation sources.

Findings

Light modes coupled to the Higgs arise from symmetry breaking

Spontaneous CP violation is common due to explicit breaking

Small explicit breaking can generate large CP-violating phases

Abstract

Little Higgs models often feature spontaneously broken extra global symmetries, which must also be explicitly broken in order to avoid massless Goldstone modes in the spectrum. We show that a possible conflict with collective symmetry breaking then implies light modes coupled to the Higgs boson, leading to interesting phenomenology. Moreover, spontaneous CP violation is quite generic in such cases, as the explicit breaking may be used to stabilize physical CP odd phases in the vacuum. We demonstrate this in an SU(2) \times SU(2) \times U(1) variant of the Littlest Higgs, as well as in an original SU(6)/SO(6) model. We show that even a very small explicit breaking may lead to large phases, resulting in new sources of CP violation in this class of models.