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
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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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An analytic energy spectrum for magnetic fields from electroweak symmetry breaking is obtained from random inhomogeneous Higgs configurations and validated with continuous-field simulations.
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.
citing papers explorer
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Wave interference as the origin of the cyclic magnetorotational dynamo in accretion disks: insights from weakly nonlinear theory and local shearing box simulations
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.
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Energy spectrum of magnetic fields from electroweak symmetry breaking
An analytic energy spectrum for magnetic fields from electroweak symmetry breaking is obtained from random inhomogeneous Higgs configurations and validated with continuous-field simulations.
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Self-Consistent Parker Bound on Magnetic Monopoles
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.