2025/03/20 by Luca Di Luzio, Di Luzio, Luca, Giacomo Landini +5
Physics and Astronomy · #Dark Matter and Cosmic Phenomena #Particle physics theoretical and experimental studies #Cosmology and Gravitation Theories
paper · pdf · doi:10.48550/arxiv.2503.16648
We explore a class of axion models where an accidental U(1) Peccei-Quinn (PQ) symmetry automatically emerges from the interplay of vertical (grand-unified) and horizontal (flavor) gauge symmetries. We study a specific Pati-Salam realization in detail, and aim to generalize the conclusions. We show that our specific model offers protection from PQ-violating operators to high dimension, and demonstrate that the model can reproduce the Standard Model flavor structure. A distinctive feature of the vertical-horizontal setup is the presence of parametrically light fermions, known as anomalons, which are introduced to cancel the gauge anomalies of the flavor symmetry. We also identify a major challenge to building a fully realistic model, most notably that of Landau poles in gauge couplings before the Planck scale. For the specific model investigated, the pre-inflationary PQ-breaking scenario predicts the axion mass window to be ma ∈ [2 × 10-8, 10-3] eV. Conversely, a high-quality axion may be obtained instead in the post-inflationary scenario, with axion mass ma \gtrsim 0.01 eV, and anomalon masses predicted below the eV scale. We elaborate on anomalons' cosmological production in the early universe, highlighting how measurements of ΔN\rm eff could serve as a low-energy probe of the ultraviolet dynamics addressing the PQ quality problem.