Title: A Grand unified solution to the Axion Quality Problem

Abstract: Invisible axion models that solve the strong CP problem via the Peccei-Quinn (PQ) mechanism typically have a quality problem that arises from quantum gravity effects which violate all global symmetries. These models therefore require extreme fine-tuning of parameters for consistency. We present a new class of solutions to the quality problem in a unified SO(10) × U(1)a gauge model, where U(1)a is an anomaly free axial gauge symmetry. PQ symmetry emerges as an accidental symmetry in this setup, which admits a PQ breaking scale as large as 4 × 1011 GeV, allowing for the axion to be the cosmological dark matter.  Furthermore, the model has no domain wall problem and it provides a realistic and predictive framework for fermion masses and mixings.