Gauge (in)dependence and background field formalism

It is shown that the gauge invariance and gauge dependence properties of effective action for Yang-Mills theories should be considered as two independent issues in the background field formalism. Application of this formalism to formulate the functional renormalization group approach is discussed. It is proven that there is a possibility to construct the corresponding average effective action invariant under the gauge transformations of background vector field. Nevertheless, being gauge invariant this action remains gauge dependent on-shell.Comment: 14 pages, v2: typos corrected, v3:minor correction in Eqs. (2.24), v4: a reference added, misprints corrected, accepted for publication in PL

The Effects of Burst Activity on Soft Gamma Repeater Pulse Properties and Persistent Emission

Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and persistent emission during episodes of intense burst activity. SGR 1900+14 has undergone large flux increases following recent burst activity. Both SGR 1900+14 and SGR 1806-20 have shown significant changes in their pulse profile and spin-down rates during the last several years. The pulse profile changes are linked with the burst activity whereas the torque variations are not directly correlated with the bursts. Here, we review the observed dynamics of the pulsed and persistent emission of SGR 1900+14 and SGR 1806-20 during burst active episodes and discuss what implications these results have for the burst emission mechanism, the magnetic field dynamics of magnetars, the nature of the torque variability, and SGRs in general.Comment: 9 pages, Woods Hole 2001 GRB and SGR Conferenc

Mass Media and Environmental Risk: Seven Principles

Dr. Sandman suggests that, when spokespersons for risk sources are inept in conveying their messages, they and we pay heavily for their mistakes