Radiative transfer dynamo effect

Magnetic fields in rotating and radiating astrophysical plasma can be produced due to a radiative interaction between plasma layers moving relative to each other. The efficiency of current drive, and with it the associated dynamo effect, is considered in a number of limits. It is shown here, however, that predictions for these generated magnetic fields can be significantly higher when kinetic effects, previously neglected, are taken into account.Comment: 6 pages, 4 figures, published in Physical Review

Algebraic Properties of BRST Coupled Doublets

We characterize the dependence on doublets of the cohomology of an arbitrary nilpotent differential s (including BRST differentials and classical linearized Slavnov-Taylor (ST) operators) in terms of the cohomology of the doublets-independent component of s. All cohomologies are computed in the space of local integrated formal power series. We drop the usual assumption that the counting operator for the doublets commutes with s (decoupled doublets) and discuss the general case where the counting operator does not commute with s (coupled doublets). The results are purely algebraic and do not rely on power-counting arguments.Comment: Some explanations enlarged, references adde

Random Field and Random Anisotropy Effects in Defect-Free Three-Dimensional XY Models

Monte Carlo simulations have been used to study a vortex-free XY ferromagnet with a random field or a random anisotropy on simple cubic lattices. In the random field case, which can be related to a charge-density wave pinned by random point defects, it is found that long-range order is destroyed even for weak randomness. In the random anisotropy case, which can be related to a randomly pinned spin-density wave, the long-range order is not destroyed and the correlation length is finite. In both cases there are many local minima of the free energy separated by high entropy barriers. Our results for the random field case are consistent with the existence of a Bragg glass phase of the type discussed by Emig, Bogner and Nattermann.Comment: 10 pages, including 2 figures, extensively revise

BRST-anti-BRST Antifield formalism : The Example of the Freedman-Townsend Model

The general BRST-anti-BRST construction in the framework of the antifield-antibracket formalism is illustrated in the case of the Freedmann-Townsend model.Comment: 16 pages, Latex file, Latex errors corrected, otherwise unchange

Randomly Dilute Two Dimensional Ising Models

Calculations of the specific heat and magnetization of quenched, site‐diluted, N×N square and triangular Ising lattices have been carried out by a Monte Carlo method. For spin concentrations x of 0.8 and 0.9, lattices of size N=64 did not give sharp transitions. For a triangular lattice with N=128 and x=0.904, we found a well‐defined peak in the specific heat and an abrupt change in the magnetization at T=0.865 Tc(1). Linear interpolation gives s≡d/dx[Tc(x)/Tc(1)]x=1=1.40±0.05, in excellent agreement with the high temperature series calculations of Rushbrooke et al. For the square lattice we calculate s=1.5±0.1. We also determined site magnetization as a function of the number of ’’live’’ nearest neighbors