Axion from pseudo Goldstone seesaw without Peccei-Quinn symmetry

Abstract

It is firmly believed that the axion for solving the strong CP problem must come from the spontaneous breaking of an anomalous Peccei-Quinn global symmetry. Here we show a new possibility that the axion can be induced by a pseudo Goldstone seesaw mechanism although the Peccei-Quinn symmetry is exactly forbidden. Specifically, after the spontaneous breaking of appropriate gauge and discrete symmetries, a heavy pseudo Goldstone coupling to colored fermions is allowed to have a tiny mass mixing with an ultralight pseudo Goldstone. In our scenario, no symmetry breaking is required to happen above the TeV scale. This means rich collider phenomena to explore the origin of axion.