High-Scale Axions without Isocurvature from Inflationary Dynamics

Abstract

Observable primordial tensor modes in the cosmic microwave background (CMB) would point to a high scale of inflation $H_I$. If the scale of Peccei-Quinn (PQ) breaking $f_a$ is greater than $\frac{H_I}{2\pi }$, CMB constraints on isocurvature naively rule out QCD axion dark matter. This assumes the potential of the axion is unmodified during inflation. We revisit models where inflationary dynamics modify the axion potential and discuss how isocurvature bounds can be relaxed. We find that models that rely solely on a larger PQ-breaking scale during inflation $f_I$ require either late-time dilution of the axion abundance or highly super-Planckian $f_I$ that somehow does not dominate the inflationary energy density. Models that have enhanced explicit breaking of the PQ symmetry during inflation may allow $f_a$ close to the Planck scale. Avoiding disruption of inflationary dynamics provides important limits on the parameter space.

21 pages, 5 figures; v2: strengthened bounds in Sec. IIA, references added, published version

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Cited by in corpus (16)

• Opening up the QCD axion window
• Axion Misalignment Driven to the Bottom
• The meso-inflationary QCD axion
• Axion Isocurvature Perturbations in Low-Scale Models of Hybrid Inflation
• Diraxiogenesis
• New mechanism for primordial black hole formation from the QCD axion
• Revisiting Isocurvature Bounds on the Minimal QCD Axion
• Cosmological Perturbations of Axion with a Dynamical Decay Constant
• Opening up a window on the postinflationary QCD axion
• Minimal solution to the axion isocurvature problem from a nonminimal coupling
• A Dynamical Solution to the Axion Domain Wall Problem
• Non-thermal Axion Dark Radiation and Constraints
• Higgs-dilaton model revisited: can dilaton act as QCD axion?
• Ultraviolet Sensitivity of Peccei-Quinn Inflation
• An Analytic Treatment of Underdamped Axionic Blue Isocurvature Perturbations
• Kination cosmology from scalar fields and gravitational-wave signatures