Planck Limits on Non-canonical Generalizations of Large-field Inflation Models

Abstract

In this paper, we consider two case examples of Dirac-Born-Infeld (DBI) generalizations of canonical large-field inflation models, characterized by a reduced sound speed, $c_S<1$. The reduced speed of sound lowers the tensor-scalar ratio, improving the fit of the models to the data, but increases the equilateral-mode non-Gaussianity, $f_{\mathrm{NL}}^{equil.}$, which the latest results from the Planck satellite constrain by a new upper bound. We examine constraints on these models in light of the most recent Planck and BICEP/Keck results, and find that they have a greatly decreased window of viability. The upper bound on $f_{\mathrm{NL}}^{equil.}$ corresponds to a lower bound on the sound speed and a corresponding lower bound on the tensor-scalar ratio of $r\sim 0.01$, so that near-future Cosmic Microwave Background observations may be capable of ruling out entire classes of DBI inflation models. The result is, however, not universal: infrared-type DBI inflation models, where the speed of sound increases with time, are not subject to the bound.

arXiv comment20 pages, 4 figures (v2: references added, version to appear in JCAP)

References in corpus (44)

• Planck 2015 results. XIII. Cosmological parameters
• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• k-Inflation
• The Effective Field Theory of Inflation
• DBI in the Sky
• Encyclopaedia Inflationaris
• Observational Signatures and Non-Gaussianities of General Single Field Inflation
• What would we learn by detecting a gravitational wave signal in the cosmic microwave background anisotropy?
• Scalar Speed Limits and Cosmology: Acceleration from D-cceleration
• Planck 2015 results. XI. CMB power spectra, likelihoods, and robustness of parameters
• Formalising the Slow-Roll Approximation in Inflation
• Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
• Planck 2015 results. XVII. Constraints on primordial non-Gaussianity
• Inflation after WMAP3: Confronting the Slow-Roll and Exact Power Spectra with CMB Data
• Equilateral Non-Gaussianity and New Physics on the Horizon
• Warm Little Inflaton
• Inflation from Warped Space
• Comments on the Starobinsky Model of Inflation and its Descendants
• Inflation: flow, fixed points and observables to arbitrary order in slow roll
• Inflation model constraints from the Wilkinson Microwave Anisotropy Probe three-year data
• Multi-Throat Brane Inflation
• Cosmic microwave background measurements can discriminate among inflation models
• Signs of Analyticity in Single-Field Inflation
• More hilltop inflation models
• Phenomenology of D-Brane Inflation with General Speed of Sound
• BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array
• Constraining Inflation with Cosmic Microwave Background Polarization
• Coleman-Weinberg Inflation in light of Planck
• Effective field theory of weakly coupled inflationary models
• Quantum modes in DBI inflation: exact solutions and constraints from vacuum selection
• B-modes and the Nature of Inflation
• Inflation models after WMAP year three
• Tachyacoustic Cosmology: An Alternative to Inflation
• Inflation model constraints from data released in 2015
• Eternal Hilltop Inflation
• A Consistency Relation for Power Law Inflation in DBI models
• Non-canonical generalizations of slow-roll inflation models
• Inflation with an extra light scalar field after Planck
• On the Slow Roll Expansion for Brane Inflation
• Bridging geometries and potentials in DBI cosmologies
• On the Three Primordial Numbers
• Effects of the speed of sound at large-N
• Limits on Entanglement Effects in the String Landscape from Planck and BICEP/Keck Data
• B-modes and the sound speed of primordial fluctuations

Cited by in corpus (9)

• The zoo plot meets the swampland: mutual (in)consistency of single-field inflation, string conjectures, and cosmological data
• Brane Constant-roll Inflation
• Warm Tachyon Inflation and Swampland Criteria
• Beta-function formalism for k-essence constant-roll inflation
• Inflation with non-canonical scalar fields revisited
• Trans-Planckian Censorship and $k$-inflation
• Dark Matter Freeze-In and Small-Scale Observables: Novel Mass Bounds and Viable Particle Candidates
• Flattened Axion Monodromy Beyond Two Derivatives
• Constraints on non-canonical chaotic inflation from ACT DR6 and BICEP/Keck data