Natural Inflation: Consistency with Cosmic Microwave Background Observations of Planck and BICEP2

Abstract

Natural inflation is a good fit to all cosmic microwave background (CMB) data and may be the correct description of an early inflationary expansion of the Universe. The large angular scale CMB polarization experiment BICEP2 has announced a major discovery, which can be explained as the gravitational wave signature of inflation, at a level that matches predictions by natural inflation models. The natural inflation (NI) potential is theoretically exceptionally well motivated in that it is naturally flat due to shift symmetries, and in the simplest version takes the form $V(\varphi )={\Lambda }^4[1\pm \cos (N\varphi /f)]$. A tensor-to-scalar ratio $r>0.1$ as seen by BICEP2 requires the height of any inflationary potential to be comparable to the scale of grand unification and the width to be comparable to the Planck scale. The Cosine Natural Inflation model agrees with all cosmic microwave background measurements as long as $f\ge m_{\mathrm{Pl}}$ (where $m_{\mathrm{Pl}}=1.22\times 10^{19}\mathrm{GeV}$) and $\Lambda \sim m_{\mathrm{GUT}}\sim 10^{16}\mathrm{GeV}$. This paper also discusses other variants of the natural inflation paradigm: we show that axion monodromy with potential $V\propto {\varphi }^{2/3}$ is inconsistent with the BICEP2 limits at the 95\% confidence level, and low-scale inflation is strongly ruled out. Linear potentials $V\propto \varphi$ are inconsistent with the BICEP2 limit at the 95\% confidence level, but are marginally consistent with a joint Planck/BICEP2 limit at 95\%. We discuss the pseudo-Nambu Goldstone model proposed by Kinney and Mahanthappa as a concrete realization of low-scale inflation. While the low-scale limit of the model is inconsistent with the data, the large-field limit of the model is marginally consistent with BICEP2. All of the models considered predict negligible running of the scalar spectral index, and would be ruled out by a detection of running.

arXiv admin note: substantial text overlap with arXiv:hep-ph/0609144 v3: Version submitted to JCAP

References in corpus (17)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Monodromy in the CMB: Gravity Waves and String Inflation
• Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
• A Natural Framework for Chaotic Inflation
• Toward an Understanding of Foreground Emission in the BICEP2 Region
• Reheating constraints to inflationary models
• Inflation after WMAP3: Confronting the Slow-Roll and Exact Power Spectra with CMB Data
• An Ignoble Approach to Large Field Inflation
• Inflation model constraints from the Wilkinson Microwave Anisotropy Probe three-year data
• A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty
• UV-Protected Inflation
• Axion Inflation in Type II String Theory
• Relic Neutrinos, thermal axions and cosmology in early 2014
• Multi-Natural Inflation in Supergravity
• Natural Inflation: status after WMAP 3-year data
• Inflation models after WMAP year three
• Natural Inflation: the status after WMAP 3-year data

Cited by in corpus (23)

• Primordial Gravitational Waves from Axion-Gauge Fields Dynamics
• Interacting neutrinos in cosmology: exact description and constraints
• Inflation meets neutrinos
• Observational Constraints on Warm Natural Inflation
• Natural inflation with and without modulations in type IIB string theory
• Swampland conjectures in hybrid metric-Palatini gravity
• Study of Goldstone Inflation in the domain of Einstein-Gauss-Bonnet gravity
• Natural Milli-Charged Inflation
• Gravitational waves detectable in laser interferometers from axion-SU(2) inflation
• The History of Inflation from Microwave Background Polarimetry and Laser Interferometry
• Measuring inflaton couplings via dark radiation as $\Delta N_{\mathrm{eff}}$ in CMB
• Perspective on completing natural inflation
• Natural Inflation from Polymer Quantization
• The reheating constraints to natural inflation in Horndeski gravity
• Natural inflation with natural number of e-foldings
• Effect of Dissipation on Warm Chromo-Natural Inflation
• Primordial blackholes from Gauss-Bonnet-corrected single field inflation
• Implications of pulsar timing arrays for Gauss-Bonnet Inflation
• Generalized hybrid natural inflation
• Universe bouncing its way to inflation
• Reheating constraints and the $H_0$ tension in Quintessential Inflation
• Inflation and Primordial Perturbations in Fractal Cosmology
• A Tachyon Field around the Black Hole