Brownian Axion-like particles

Abstract

We study the non-equilibrium dynamics of a pseudoscalar axion-like particle (ALP) weakly coupled to degrees of freedom in thermal equilibrium by obtaining its reduced density matrix. Its time evolution is determined by the in-in effective action which we obtain to leading order in the (ALP) coupling but to \emph{all orders} in the couplings of the bath to other fields within or beyond the standard model. The effective equation of motion for the (ALP) is a Langevin equation with noise and friction kernels obeying the fluctuation dissipation relation. A ``misaligned'' initial condition yields damped coherent oscillations, however, the (ALP) population increases towards thermalization with the bath. As a result, the energy density features a mixture of a cold component from misalignment and a hot component from thermalization with proportions that vary in time $(cold)e^{-\Gamma t}+(hot)(1-e^{-\Gamma t})$, providing a scenario wherein the ``warmth'' of the dark matter evolves in time from colder to hotter. As a specific example we consider the (ALP)-photon coupling $ga\vec{E}\cdot \vec{B}$ to lowest order, valid from recombination onwards. For $T\gg m_a$ the long-wavelength relaxation rate is substantially enhanced ${\Gamma }_T=\frac{g^2{m}_a^{2}T}{16\pi }$. The ultraviolet divergences of the (ALP) self-energy require higher order derivative terms in the effective action. We find that at high temperature, the finite temperature effective mass of the (ALP) is $m_a^2(T)=m_a^2(0)[1-(T/T_c{)}^4]$, with $T_c\propto \sqrt{m_a(0)/g}$, \emph{suggesting} the possibility of an inverted phase transition, which when combined with higher derivatives may possibly indicate exotic new phases. We discuss possible cosmological consequences on structure formation, the effective number of relativistic species and birefringence of the cosmic microwave background.

arXiv commentpublished version

References in corpus (31)

• Axion Cosmology
• Cold and Fuzzy Dark Matter
• Ultralight scalars as cosmological dark matter
• New CAST Limit on the Axion-Photon Interaction
• Experimental Searches for the Axion and Axion-like Particles
• Thermal Production of Gravitinos
• Dissipation via Particle Production in Scalar Field Theories
• Invisible Axion Search Methods
• Couplings and Scales in Strongly Coupled Heterotic String Theory
• Search for "Invisible" Axion Dark Matter in the $3.3\text{-}4.2\mu$eV Mass Range
• Quantum Fluctuations, Decoherence of the Mean Field, and Structure Formation in the Early Universe
• New physics from the polarised light of the cosmic microwave background
• On Axion Thermalization in the Early Universe
• Radiation reaction and gravitational waves in the effective field theory approach
• An effective field theory during inflation: reduced density matrix and its quantum master equation
• Stochastic dynamics of correlations in quantum field theory: From Schwinger-Dyson to Boltzmann-Langevin equation
• Stochastic description for open quantum systems
• Stochastic interpretation of Kadanoff-Baym equations and their relation to Langevin processes
• An ultralight pseudoscalar boson
• Non-Markovian Dynamics of Open Quantum Systems: Stochastic Equations and their Perturbative Solutions
• Effective Field Theory out of Equilibrium: Brownian quantum fields
• Dynamical evolution of axion condensates under stimulated decays into photons
• Particle abundance in a thermal plasma: quantum kinetics vs. Boltzmann equation
• How to suppress exponential growth -- on the parametric resonance of photons in an axion background
• The Lifshitz Regime and its Experimental Signals
• New astrophysical bounds on ultralight axionlike particles
• Photon Production of Axionic Cold Dark Matter
• Particle decay in post inflationary cosmology
• A path integral approach to the Langevin equation
• Cosmological decay of Higgs-like scalars into a fermion channel
• Derivation of the fluctuation-dissipation theorem from unitarity

Cited by in corpus (9)

• Non-equilibrium dynamics of Axion-like particles: the quantum master equation
• A Quantum Description of Wave Dark Matter
• Is the finite temperature effective potential, effective for dynamics?
• Chern Simons condensate from misaligned axions
• Synthetic and cosmological axion hybridization: entangled photons, (HBT) and quantum beats
• Effective field theory of particle mixing
• Dynamics of axion-neutral pseudoscalar mixing
• Field mixing in a thermal medium: A quantum master equation approach
• Condensate decay in a radiation dominated cosmology