Spontaneous CP violation and light particles in the littlest Higgs models

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) x SU(2) x 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.