Anharmonic Effects on the Squeezing of Axion Perturbations

Abstract

It is assumed in standard cosmology that the Universe underwent a period of inflation in its earliest phase, providing the seeds for structure formation through vacuum fluctuations of the inflaton scalar field. These fluctuations get stretched by the quasi-exponential expansion of the Universe and become squeezed. The aim of this paper is to deepen the understanding of the squeezing process, considering the effect of self-interactions. Axion-like particles can provide a useful setup to study this effect. Specifically we focus on the consequences that a non-trivial evolution of the background axion field has on the squeezing of the perturbations. We follow the evolution of the axion's fluctuation modes from the horizon exit during inflation to the radiation-dominated epoch. We compute Bogoliubov coefficients and squeezing parameters, which are linked to the axion particle number and isocurvature perturbation. We find that the quantum mechanical particle production and the squeezing of the perturbations are enhanced, if one accounts for anharmonic effects, i.e., the effect of higher order terms in the potential. This effect becomes particularly strong towards the hilltop of the potential.

arXiv comment22 pages + appendices, 10 figures

References in corpus (29)

• Semiclassicality and Decoherence of Cosmological Perturbations
• Leggett-Garg Inequalities
• Inflation and squeezed quantum states
• Lyman-alpha Constraints on Ultralight Scalar Dark Matter: Implications for the Early and Late Universe
• Decoherence during Inflation: the generation of classical inhomogeneities
• Update of axion CDM energy density
• Quantum Discord of Cosmic Inflation: Can we Show that CMB Anisotropies are of Quantum-Mechanical Origin?
• On the Decoherence of Primordial Fluctuations During Inflation
• Inflationary Perturbations: the Cosmological Schwinger Effect
• Relic Gravitational Waves and Cosmology
• Squeezed Vacua and the Quantum Statistics of Cosmological Particle Creation
• Signals of a Quantum Universe
• On the Decoherence of Primordial Fluctuations During Inflation
• Obstructions to Bell CMB Experiments
• Non-Gaussianity from Curvatons Revisited
• Isocurvature Constraints and Anharmonic Effects on QCD Axion Dark Matter
• Emergence of classicality for primordial fluctuations: Concepts and analogies
• Is the squeezing of relic gravitational waves produced by inflation detectable?
• Discord and Decoherence
• Non Gaussianities from Quantum Decoherence during Inflation
• Decoherence and entropy of primordial fluctuations. I: Formalism and interpretation
• Anharmonic Evolution of the Cosmic Axion Density Spectrum
• Decoherence and entropy of primordial fluctuations II. The entropy budget
• Cosmic decoherence: primordial power spectra and non-Gaussianities
• Comparing quantumness criteria
• No intrinsic decoherence of inflationary cosmological perturbations
• Squeezing the Axion
• Squeezed quantum states of graviton and axion in the universe
• Amplifying quantum discord during inflationary magnetogenesis through violation of parity