4 research outputs found
Spectra of Magnetic Fields Injected during Baryogenesis
Helical magnetic fields are injected into the cosmic medium during
cosmological baryogenesis and can potentially provide a useful probe of the
early universe. We construct a model to study the injection process during a
first order phase transition and to determine the power spectra of the injected
magnetic field. By Monte Carlo simulations we evaluate the Fourier space
symmetric and helical power spectra of the magnetic field at the time the phase
transition completes. The spectra are peaked at the scale given by the inverse
size of bubbles at percolation and with a comparable width. These injected
magnetic fields set the initial conditions for further cosmological
magneto-hydrodynamical evolution.Comment: 8 pages, 9 figures; revised discussion and added new references;
version accepted for publication in PR
It's Hard to Learn How Gravity and Electromagnetism Couple
We construct the most general effective Lagrangian coupling gravity and
electromagnetism up to mass dimension 6 by enumerating all possible non-minimal
coupling terms respecting both diffeomorphism and gauge invariance. In all,
there are only two unique terms after field re-definitions; one is known to
arise from loop effects in QED while the other is a parity violating term which
may be generated by weak interactions within the standard model of particle
physics. We show that neither the cosmological propagation of light nor,
contrary to earlier claims, solar system tests of General Relativity are useful
probes of these terms. These non-minimal couplings of gravity and
electromagnetism may remain a mystery for the foreseeable future.Comment: 9 pages. Minor corrections made. To appear in Phys. Rev.