Nonclassicality of axion-like dark matter through gravitational self-interactions

Abstract

Axion-like particles (ALPs) are promising dark matter candidates. They are typically described by a classical field, motivated by large phase space occupation numbers. Here we show that such a description is accompanied by a quantum effect: squeezing due to gravitational self-interactions. For a typical QCD axion today, the onset of squeezing is reached on $\mu \mathrm{s}$-scales and grows over millennia. Thus within the usual models based on the classical Schrödinger-Poisson equation, a type of Gross-Pitaevskii equation, any viable ALP is nonclassical. We also show that squeezing may be relevant on the scales of other self-gravitating systems such as galactic haloes, or solitonic cores. Conversely, our results highlight the incompleteness and limitations of the classical single field description of ALPs.

13 pages, 3 figures, extended discussion and minor changes

References in corpus (20)

• Quantum computational advantage using photons
• Ultralight scalars as cosmological dark matter
• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• Nonlinear atom interferometer surpasses classical precision limit
• Understanding the Core-Halo Relation of Quantum Wave Dark Matter, $\psi$DM, from 3D Simulations
• Bose-Einstein Condensation of Dark Matter Axions
• A quantum-enhanced search for dark matter axions
• Wave Dark Matter
• The multi-configurational time-dependent Hartree method for bosons: Many-body dynamics of bosonic systems
• Invisible Axion Search Methods
• Spin squeezing, entanglement and quantum metrology with Bose-Einstein condensates
• Best mean-field for condensates
• Solving the Vlasov equation in two spatial dimensions with the Schrödinger method
• Quantum and Classical Behavior in Interacting Bosonic Systems
• Generating squeezing in an atom laser through self-interaction
• Time-dependent multi-orbital mean-field for fragmented Bose-Einstein condensates
• Extremal quantum states
• Quantum-field dynamics of expanding and contracting Bose-Einstein condensates
• Squeezing the Axion
• On the single classical field description of interacting scalar fields

Cited by in corpus (2)

• On inference of quantization from gravitationally induced entanglement
• When quantum corrections alter the predictions of classical field theory for scalar field dark matter