Wave interference from beats between nearly degenerate MRI eigenfrequencies drives cyclic large-scale dynamos in unstratified accretion disks via an oscillating shear-current effect, predicting a period of ~30(1+a²)^{1/2} orbital times.
Astrophysical magnetic fields and nonlinear dynamo theory
11 Pith papers cite this work. Polarity classification is still indexing.
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abstract
The current understanding of astrophysical magnetic fields is reviewed, focusing on their generation and maintenance by turbulence. In the astrophysical context this generation is usually explained by a self-excited dynamo, which involves flows that can amplify a weak 'seed' magnetic field exponentially fast. Particular emphasis is placed on the nonlinear saturation of the dynamo. Analytic and numerical results are discussed both for small scale dynamos, which are completely isotropic, and for large scale dynamos, where some form of parity breaking is crucial. Central to the discussion of large scale dynamos is the so-called alpha effect which explains the generation of a mean field if the turbulence lacks mirror symmetry, i.e. if the flow has kinetic helicity. Large scale dynamos produce small scale helical fields as a waste product that quench the large scale dynamo and hence the alpha effect. With this in mind, the microscopic theory of the alpha effect is revisited in full detail and recent results for the loss of helical magnetic fields are reviewed.
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A Runge-Kutta-Gegenbauer super-time-stepping method for stable, efficient handling of anisotropic non-ideal MHD diffusion.
An analytic energy spectrum for magnetic fields from electroweak symmetry breaking is obtained from random inhomogeneous Higgs configurations and validated with continuous-field simulations.
High-resolution GR neutrino-radiation MHD simulation of 1.35-1.35 Msun BNS merger shows KHI-driven B-field amplification to magnetar levels (~10^50 erg, factor >=316) in 3 ms post-merger.
A self-consistent Parker bound on magnetic monopoles is derived using the galactic mean-field dynamo eigenmode and turbulent field seeding and acceleration, producing modified flux limits at low and intermediate masses that are robust to primordial magnetic fields.
A symbiotic axion-dilaton system sources a moderately chiral dark U(1) magnetic field of astrophysically relevant strength during radiation domination through tachyonic amplification without fine-tuning.
MHD simulations indicate that SKA-Mid Band 5a can detect filamentary polarized emission from ICM magnetic fields at high resolution and sensitivity, allowing inference of turbulence driving scales.
Proposes SKA surveys for a census of galactic magnetic fields from low to high redshift using polarimetry, RM grids, and lensed quasars to constrain dynamo models.
A review chapter summarizing theoretical 21-cm signatures from Cosmic Dawn and Reionization and their detectability with SKA-Low.
FRBs serve as cosmological probes via dispersion measure, scattering, and Faraday rotation to constrain baryon distribution, expansion history, magnetic fields, and fundamental physics effects.
Literature review summarizing observations, theoretical models, and MHD simulations of the small-scale solar dynamo operating in the solar photosphere and convection zone.
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A robust super-time-stepping scheme for Ohmic and ambipolar diffusion
A Runge-Kutta-Gegenbauer super-time-stepping method for stable, efficient handling of anisotropic non-ideal MHD diffusion.