Nonminimal Couplings and the Forgotten Field of Axion Inflation
arXiv:2010.04179
Abstract
We study the multifield dynamics of axion models nonminimally coupled to gravity. As usual, we consider a canonical symmetry-breaking model in which the axion is the phase of a complex scalar field. If the complex scalar field has a nonminimal coupling to gravity, then the (oft-forgotten) radial component can drive a phase of inflation prior to an inflationary phase driven by the axion field. In this setup, the mass of the axion field is dependent on the radial field because of the nonminimal coupling, and the axion remains extremely light during the phase of radial inflation. As the radial field approaches the minimum of its potential, there is a transition to a second phase of inflation during which the axion field contributes a substantial fraction of the system's total energy density, yielding a phase of "natural inflation." This system exhibits ultra-light isocurvature perturbations, which are converted to adiabatic perturbations by a turning field-space trajectory. For models wherein the CMB pivot scale exited the horizon well before the turn, this acts to suppress the tensor-to-scalar ratio , without generating CMB non-Gaussianity or observable isocurvature perturbations. Finally, we note that for certain parameters the interaction strength between axion and gauge fields can be suppressed during the first phase of inflation relative to its value during the second phase by several orders of magnitude. This decouples the constraints on the inflationary production of gauge fields (e.g., from primordial black holes) from the constraints on their production during (p)reheating.
arXiv comment17 pages, 12 figures. v2: 19 pages, 13 figures. Updated and extended to include new parameter examples and dynamics
References in corpus (40)
- The Standard Model Higgs boson as the inflaton
- String Axiverse
- The Simons Observatory: Science goals and forecasts
- Hybrid Inflation
- False Vacuum Inflation with Einstein Gravity
- Monodromy in the CMB: Gravity Waves and String Inflation
- A new approach to the evolution of cosmological perturbations on large scales
- Gravity Waves and Linear Inflation from Axion Monodromy
- Adiabatic and entropy perturbations from inflation
- Primordial Non-Gaussianities from Inflation Models
- How long before the end of inflation were observable perturbations produced?
- The type IIB string axiverse and its low-energy phenomenology
- Minimal Supergravity Models of Inflation
- The Unity of Cosmological Attractors
- Naturally inflating on steep potentials through electromagnetic dissipation
- Primordial Spectral Indices from Generalized Einstein Theories
- Perturbations in generalized multi-field inflation
- Complete constraints on a nonminimally coupled chaotic inflationary scenario from the cosmic microwave background
- Multifield Inflation after Planck: The Case for Nonminimal Couplings
- Generalised constraints on the curvature perturbation from primordial black holes
- Conformal Transformations with Multiple Scalar Fields
- Magnetogenesis from axion inflation
- Primordial Bispectrum from Multifield Inflation with Nonminimal Couplings
- Observational consequences of chaotic inflation with nonminimal coupling to gravity
- A Horizon Ratio Bound for Inflationary Fluctuations
- Density perturbations in generalized Einstein scenarios and constraints on nonminimal couplings from the Cosmic Microwave Background
- Constraining axion inflation with gravitational waves from preheating
- A covariant approach to general field space metric in multi-field inflation
- Constraining axion inflation with gravitational waves across 29 decades in frequency
- Multifield Inflation after Planck: Isocurvature Modes from Nonminimal Couplings
- A Simple Method for One-Loop Renormalization in Curved Space-Time
- Standard Clock in Primordial Density Perturbations and Cosmic Microwave Background
- Scaling attractors in multi-field inflation
- Multi-field inflation and cosmological perturbations
- A crucial ingredient of inflation
- Hypernatural inflation
- Preheating and Entropy Perturbations in Axion Monodromy Inflation
- A Direct Probe of the Evolutionary History of the Primordial Universe
- Testing Two-Field Inflation
- Spectral Distortions of the CMB as a Probe of Inflation, Recombination, Structure Formation and Particle Physics