Abstract
We study the dynamics of the Peccei-Quinn (PQ) phase transition for the QCD axion. In weakly coupled models the transition is typically second order except in the region of parameters where the PQ symmetry is broken through the Coleman-Weinberg mechanism. In strongly coupled realizations the transition is often first order. We show examples where the phase transition leads to strong supercooling lowering the nucleation temperature and enhancing the stochastic gravitational wave signals. The models predict a frequency peak in the range 100–1000 Hz with an amplitude that is already within the sensitivity of LIGO and can be thoroughly tested with future gravitational wave interferometers.
Highlights
After showing that in KSVZ models the phase transition is second order, we show that in theories with massless scalars the PQ symmetry is broken through the Coleman-Weinberg mechanism leading to a first order phase transition
We discuss the realization of this mechanism in spontaneously broken strongly-coupled conformal field theories and their dual Randall-Sundrum-like incarnations. In both cases we find that the GW signal is within the reach of present and future Earth-based GW interferometers such as LIGO/VIRGO and the Einstein Telescope (ET)
In this work we have shown that a new and complementary information on the physics of the QCD axion may come from the study of GWs produced during the PQ phase transition
Summary
We study axion models that are described in terms of fundamental scalars at all energy scales. We analyze two classes of theories: models of KSVZ type, and models in which the breaking of the PQ symmetry is radiatively induced.
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