By introducing a new kind of variable we find simple Lagrangian and Hamiltonian descriptions of a classical particle interacting with an external non-Abelian gauge field. Both conventional particles and supersymmetric particles carrying pseudoclassical spin are considered. The physical interpretation of these models is discussed. The models are quantized fo!lowing Dirac's procedure. Finally, the isospin representations to which the resulting quantized particles belong are investigated.
The QED effective action at finite temperature and density is calculated to all orders in an external homogeneous and time-independent magnetic field in the weak coupling limit. The free energy, obtained explicitly, exhibit the expected de Haas -van Alphen oscillations. An effective coupling at finite temperature and density is derived in a closed form and is compared with renormalization group results.
Using a consistent quantum-mechanical treatment for the electromagnetic radiation, we theoretically investigate the magnetic spin-flip scatterings of a neutral two-level atom trapped in the vicinity of a superconducting body. We derive a simple scaling law for the corresponding spin-flip lifetime for such an atom trapped near a superconducting thick slab. For temperatures below the superconducting transition temperature Tc, the lifetime is found to be enhanced by several orders of magnitude in comparison to the case of a normal conducting slab. At zero temperature the spin-flip lifetime is given by the unbounded free-space value.
The one-loop effective action for a slowly varying electromagnetic field is computed at finite temperature and density using a real-time formalism.We discuss the gauge invariance of the result. Corrections to the Debye mass from an electric field are computed at high temperature and high density. The effective coupling constant, defined from a purely electric weak-field expansion, behaves at high temperature very differently from the case of a magnetic field, and does not satisfy the renormalization group equation. The issue of pair production in the real-time formalism is discussed and also its relevance for heavy-ion collisions. 1
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