Revisiting small-scale fluctuations in $\alpha$-attractor models of inflation

Abstract

Cosmological $\alpha$-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate $\alpha$-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. We study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space. In the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non geodesic motion in field space. The two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. These enhanced scalar perturbations can lead to primordial black hole (PBH) production and second-order gravitational wave (GW) generation. Due to the existence of universal predictions in $\alpha$-attractors, consistency with current CMB constraints on the large-scale spectral tilt implies that PBHs can only be produced with masses smaller than $10^8\text{g}$ and are accompanied by ultra-high frequency GWs, with a peak expected to be at frequencies of order $10\text{kHz}$ or above.

63 pages, 42 figures, 3 tables. Version accepted for publication

References in corpus (52)

• BICEP / Keck XIII: Improved Constraints on Primordial Gravitational Waves using Planck, WMAP, and BICEP/Keck Observations through the 2018 Observing Season
• Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations
• The cosmological gravitational wave background from primordial density perturbations
• Primordial Non-Gaussianities from Inflation Models
• The Unity of Cosmological Attractors
• Challenges and Opportunities of Gravitational Wave Searches at MHz to GHz Frequencies
• Primordial black hole dark matter from single field inflation
• Primordial Black Holes and Slow-Roll Violation
• Generation and Characterization of Large Non-Gaussianities in Single Field Inflation
• Calculating the mass spectrum of primordial black holes
• Gravitational waves from a universe filled with primordial black holes
• Perturbations in generalized multi-field inflation
• Curvature and isocurvature perturbations in two-field inflation
• Generating PBHs and small-scale GWs in two-field models of inflation
• PBHs and secondary GWs from ultra slow roll and punctuated inflation
• Ultra slow-roll inflation demystified
• Non-Gaussianity and the induced gravitational wave background
• Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation
• Single-field inflation, anomalous enhancement of superhorizon fluctuations, and non-Gaussianity in primordial black hole formation
• The power spectrum on small scales: Robust constraints and comparing PBH methodologies
• GUT-Scale Primordial Black Holes: Consequences and Constraints
• The Formation Probability of Primordial Black Holes
• Primordial black holes in peak theory with a non-Gaussian tail
• Probing non-Gaussianities with the high frequency tail of induced gravitational waves
• Probing Primordial Features with the Stochastic Gravitational Wave Background
• Gravitational waves induced by the local-type non-Gaussian curvature perturbations
• Models of the Primordial Standard Clock
• Primordial Black Holes from Multifield Inflation with Nonminimal Couplings
• Primordial perturbations from inflation with a hyperbolic field-space
• Hybrid cosmological attractors
• Scratches from the Past: Inflationary Archaeology through Features in the Power Spectrum of Primordial Fluctuations
• Features of the inflaton potential and the power spectrum of cosmological perturbations
• Non-Gaussianity in inflationary scenarios for primordial black holes
• Resonant features in the stochastic gravitational wave background
• BICEP/Keck and Cosmological Attractors
• Polynomial $\alpha$-attractors
• GUT-Scale Primordial Black Holes: Mergers and Gravitational Waves
• The long-short wavelength mode coupling tightens primordial black hole constraints
• Uncovering the History of Cosmic Inflation from Anomalies in Cosmic Microwave Background Spectra
• Expansion history-dependent oscillations in the scalar-induced gravitational wave background
• On reaching the adiabatic limit in multi-field inflation
• Signals of primordial black holes at gravitational wave interferometers
• CMB from a Gauss-Bonnet-induced de Sitter fixed point
• Geometrical destabilization, premature end of inflation and Bayesian model selection
• Primordial Standard Clock Models and CMB Residual Anomalies
• Comparing multi-field primordial feature models with the Planck data
• Detecting primordial features with LISA
• Dilaton-Axion Inflation with PBHs and GWs
• Sharp turns in axion monodromy: primordial black holes and gravitational waves
• On backreaction effects in geometrical destabilisation of inflation
• CMB $\mu T$ cross-correlations as a probe of PBH scenarios
• Primordial blackholes from Gauss-Bonnet-corrected single field inflation

Cited by in corpus (43)

• The recent gravitational wave observation by pulsar timing arrays and primordial black holes: the importance of non-gaussianities
• Inflation and Primordial Black Holes
• Primordial non-gaussianity up to all orders: theoretical aspects and implications for primordial black hole models
• From inflation to black hole mergers and back again: Gravitational-wave data-driven constraints on inflationary scenarios with a first-principle model of primordial black holes across the QCD epoch
• Anatomy of single-field inflationary models for primordial black holes
• Questions on calculation of primordial power spectrum with large spikes: the resonance model case
• Primordial Black Holes
• Constraining Primordial Black Hole Formation from Single-Field Inflation
• Hybrid $\alpha$-attractors, primordial black holes and gravitational wave backgrounds
• Primordial Black Holes from Multifield Inflation with Nonminimal Couplings
• Primordial black holes from single-field inflation: a fine-tuning audit
• Hybrid cosmological attractors
• One loop to rule them all: Perturbativity in the presence of ultra slow-roll dynamics
• Primordial black hole dark matter from inflation: the reverse engineering approach
• Curbing PBHs with PTAs
• Constraints on primordial black holes from LIGO-Virgo-KAGRA O3 events
• Inflation, the Hubble Tension and Early Dark Energy: an alternative overview
• Primordial black holes and gravitational waves from nonminimally coupled supergravity inflation
• One-loop infrared rescattering by enhanced scalar fluctuations during inflation
• Detecting primordial features with LISA
• The Inflaton that Could : Primordial Black Holes and Second Order Gravitational Waves from Tachyonic Instability induced in Higgs-$R^2$ Inflation
• Formation of trapped vacuum bubbles during inflation, and consequences for PBH scenarios
• Dilaton-Axion Inflation with PBHs and GWs
• Gravitational wave hints black hole remnants as dark matter
• Sharp turns in axion monodromy: primordial black holes and gravitational waves
• Enhanced power on small scales and evolution of quantum state of perturbations in single and two field inflationary models
• Observing nulling of primordial correlations via the 21 cm signal
• Primordial black holes and inflation from double-well potentials
• Excess of high-$z$ galaxies as a test for bumpy power spectrum of density perturbations
• Fitting power spectrum of scalar perturbations for primordial black hole production during inflation
• The effect of multiple features on the power spectrum in two-field inflation
• Induced gravitational waves: the effect of first order tensor perturbations
• Gravity-improved metastability bounds for the Type-I Seesaw Mechanism
• Production of PBHs from inflaton structure
• Production of primordial black holes in improved E-models of inflation
• Constraining ultra slow roll inflation using cosmological datasets
• Generating large primordial fluctuations in single-field inflation for PBH formation
• Inflationary relics from an Ultra-Slow-Roll plateau
• Primordial black holes and scalar-induced gravitational waves from the polynomial attractor model
• Gravitational waves from primordial black hole dominance: The effect of inflaton decay rate
• Bayesian analysis for a class of $\alpha$-attractor inflationary models
• Inflationary $\alpha$-Attractor Models with Singular Derivative of Potential
• Development of generic no-scale inflation