Reconciling tensor and scalar observables in G-inflation

Abstract

The simple $m^2{\varphi }^2$ potential as an inflationary model is coming under increasing tension with limits on the tensor-to-scalar ratio $r$ and measurements of the scalar spectral index $n_s$. Cubic Galileon interactions in the context of the Horndeski action can potentially reconcile the observables. However, we show that this cannot be achieved with only a constant Galileon mass scale because the interactions turn off too slowly, leading also to gradient instabilities after inflation ends. Allowing for a more rapid transition can reconcile the observables but moderately breaks the slow-roll approximation leading to a relatively large and negative running of the tilt ${\alpha }_s$ that can be of order $n_s-1$. We show that the observables on CMB and large scale structure scales can be predicted accurately using the optimized slow-roll approach instead of the traditional slow-roll expansion. Upper limits on $|{\alpha }_s|$ place a lower bound of $r\gtrsim 0.005$ and conversely a given $r$ places a lower bound on $|{\alpha }_s|$, both of which are potentially observable with next generation CMB and large scale structure surveys.

arXiv commentPublished version

References in corpus (36)

• The galileon as a local modification of gravity
• Generalized G-inflation: Inflation with the most general second-order field equations
• From k-essence to generalised Galileons
• DBI in the Sky
• Monodromy in the CMB: Gravity Waves and String Inflation
• Gravity Waves and Linear Inflation from Axion Monodromy
• Scalar Speed Limits and Cosmology: Acceleration from D-cceleration
• Healthy theories beyond Horndeski
• Transforming gravity: from derivative couplings to matter to second-order scalar-tensor theories beyond the Horndeski Lagrangian
• G-inflation: inflation driven by the Galileon field
• Oscillations in the CMB from Axion Monodromy Inflation
• Degenerate higher order scalar-tensor theories beyond Horndeski up to cubic order
• Primordial Black Holes and Slow-Roll Violation
• On Inflation with Non-minimal Coupling
• Galileon inflation
• Complete constraints on a nonminimally coupled chaotic inflationary scenario from the cosmic microwave background
• Higgs G-inflation
• Observational consequences of chaotic inflation with nonminimal coupling to gravity
• Third order equations of motion and the Ostrogradsky instability
• The Spectrum of Density Perturbations produced during Inflation to Leading Order in a General Slow-Roll Approximation
• Tensor to Scalar Ratio in Non-Minimal ${\varphi }^4$ Inflation
• Duality Cascade in Brane Inflation
• Generalized Slow Roll for Large Power Spectrum Features
• Exorcising the Ostrogradsky ghost in coupled systems
• Higher Derivative Field Theories: Degeneracy Conditions and Classes
• Generalized Slow Roll for Non-Canonical Kinetic Terms
• Ghost-free theory with third-order time derivatives
• Does Current Data Prefer a Non-minimally Coupled Inflaton?
• Precision of Inflaton Potential Reconstruction from CMB Using the General Slow-Roll Approximation
• Generalized Slow Roll in the Unified Effective Field Theory of Inflation
• Complete WMAP Constraints on Bandlimited Inflationary Features
• Graceful exit from Higgs G-inflation
• Inflationary Features and Shifts in Cosmological Parameters from Planck 2015 Data
• Nonlinear Excitations in Inflationary Power Spectra
• Running from Features: Optimized Evaluation of Inflationary Power Spectra
• Generalized Slow Roll for Tensors

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• Effective field theory of degenerate higher-order inflation
• Inflation with Derivative Self-interaction and Coupling to Gravity
• Chaotic Inflation and Reheating in Generalized Scalar-Tensor Gravity
• Scalar Bispectrum Beyond Slow-Roll in the Unified EFT of Inflation
• Resonant Reconciliation of Convex Models and the Planck
• G-Warm inflation: Intermediate model
• The Black Hole Window on Cosmic Inflation