Non-equilibrium dynamics of Axion-like particles: the quantum master equation

Abstract

We study the non-equilibrium dynamics of Axion-like particles (ALP) coupled to Standard Model degrees of freedom in thermal equilibrium. The Quantum Master Equation (QME) for the (ALP) reduced density matrix is derived to leading order in the coupling of the (ALP) to the thermal bath, but to \emph{all} orders of the bath couplings to degrees of freedom within or beyond the Standard Model other than the (ALP). The (QME) describes the damped oscillation dynamics of an initial misaligned (ALP) condensate, thermalization with the bath, decoherence and entropy production within a unifying framework. The (ALP) energy density $\mathcal{E}(t)$ features two components: a ``cold'' component from the misaligned condensate and a ``hot'' component from thermalization with the bath, with $\mathcal{E}(t)={\mathcal{E}}_c{e}^{-\gamma (T)t}+{\mathcal{E}}_h(1-e^{-\gamma (T)t})$ thus providing a ``mixed dark matter'' scenario. Relaxation of the (ALP) condensate, thermalization, decoherence and entropy production occur on similar time scales. An explicit example with (ALP)-photon coupling, valid post recombination yields a relaxation rate $\gamma (T)$ with a substantial enhancement from thermal emission and absorption. A misaligned condensate is decaying at least since recombination and on the same time scale thermalizing with the cosmic microwave background (CMB). Possible consequences for birefringence of the (CMB) and (ALP) contribution to the effective number of ultrarelativistic species and galaxy formation are discussed.

28 pages

References in corpus (13)

• Ultralight scalars as cosmological dark matter
• New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data
• New physics from the polarised light of the cosmic microwave background
• Quantum Mechanics Without State Vectors
• Effective Field Theory out of Equilibrium: Brownian quantum fields
• Benchmarking the cosmological master equations
• Quantum corrections to the primordial tensor spectrum: Open EFTs & Markovian decoupling of UV modes
• Lindblad Decoherence in Atomic Clocks
• New astrophysical bounds on ultralight axionlike particles
• Axion dark matter from frictional misalignment
• Brownian Axion-like particles
• Axion dark matter with thermal friction
• Thermalization by off-shell processes: the virtues of small virtuality

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• An Open Effective Field Theory for light in a medium
• A New Solution for the Observed Isotropic Cosmic Birefringence Angle and its Implications for the Anisotropic Counterpart through a Boltzmann Approach
• Open system dynamics in interacting quantum field theories
• Chern Simons condensate from misaligned axions
• Synthetic and cosmological axion hybridization: entangled photons, (HBT) and quantum beats
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