Squeezing the Axion

Abstract

We apply the squeezed state formalism to scalar field dark matter (e.g. axion) perturbations generated during inflation. As for the inflationary perturbations, the scalar field state becomes highly squeezed as modes exit the horizon. For as long as $H>m_{\varphi }$ (with $H$ the Hubble rate and $m_{\varphi }$ the scalar mass) the scalar field field does not interact during reheating, and we follow its evolution exactly as modes re-enter the horizon. We find that the quantum state remains squeezed after horizon re-entry during the hot big bang. This demonstrates a fact well-known in the theory of inflation: cosmological observables for scalar dark matter are accurately modelled by a classical stochastic field with a fixed phase. Our calculation covers all modes smaller than the present-day cosmic de Broglie wavelength. Larger scale modes mix gravitationally with the environment when $H<m_{\varphi }$, and are thus expected to decohere.

arXiv comment8 pages, 4 figures, version accepted for publication in the Open Journal of Astrophysics

References in corpus (29)

• Axion Cosmology
• Towards the Theory of Reheating After Inflation
• String Axiverse
• Planck 2018 results. I. Overview and the cosmological legacy of Planck
• Generating the curvature perturbation without an inflaton
• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• Adiabatic and entropy perturbations from inflation
• Semiclassicality and Decoherence of Cosmological Perturbations
• Bose-Einstein Condensation of Dark Matter Axions
• Inflation and squeezed quantum states
• Do Dark Matter Axions Form a Condensate with Long-Range Correlation?
• Gravitational Bose-Einstein condensation in the kinetic regime
• Axion Cosmology and the Energy Scale of Inflation
• Cosmological Collider Physics
• The General Primordial Cosmic Perturbation
• Early seeds of axion miniclusters
• The Stochastic Axion Scenario
• Using the Full Power of the Cosmic Microwave Background to Probe Axion Dark Matter
• The QCD Axion Window and Low Scale Inflation
• First star-forming structures in fuzzy cosmic filaments
• Quantum Discord of Cosmic Inflation: Can we Show that CMB Anisotropies are of Quantum-Mechanical Origin?
• Signals of a Quantum Universe
• Intensity Mapping as a Probe of Axion Dark Matter
• Classicality and Quantum Break-Time for Cosmic Axions
• The Quantum Information of Cosmological Correlations
• Far from equilibrium dynamics of Bose-Einstein condensation for Axion Dark Matter
• Duration of classicality in highly degenerate interacting Bosonic systems
• Axion Structure Formation I: The Co-motion Picture
• Axion Structure Formation II: The Wrath of Collapse

Cited by in corpus (6)

• On inference of quantization from gravitationally induced entanglement
• Ultra-light axions and the kinetic Sunyaev-Zel'dovich Effect
• Conversion of squeezed gravitons into photons during inflation
• Nonclassicality of axion-like dark matter through gravitational self-interactions
• Primordial cosmic complexity and effects of reheating
• Anharmonic Effects on the Squeezing of Axion Perturbations