Theory of stability of large amplitude periodic /BGK/ waves in collisionless plasmas

Stability theory of large amplitude periodic BGK waves in collisionless plasmas using distribution function

Origin of spontaneous violation of the Lorentz symmetry: Vortices in the cosmos

By carefully studying the (1,0)+(0,1) representation space for massive particles we point to the existence of certain inherent tachyonic dispersion relations: E^2= p^2-m^2. We put forward an interpretation that exploits these ``negative mass squared'' solutions; rotational invariance is spontaneously broken. Relevance of these results to the vortices in the cosmos is pointed out. NOTE: Just as "negative energy solutions'' of Dirac equation are re-interpreted as antiparticles, similarly the possibility exists for re-interpreting the tachyonic dispersion relations of all (j,0)+(0,j) representation spaces via spontaneous Lorentz symmetry breaking. In Mod. Phys. Lett. A8:2623-2630,1993 we exhibited this explicitly for the j=1 representation space. The interest in this old subject has grown markedly in recent years as is evident from numerous theoretical and phenomenological works on the subject. With this observation, we make this replacement of our paper fourteen years after its initial publication. The Abstract and main text remain unaltered. The title is changed to reflect the underlying physics more closely.Comment: This is an exact copy of the published paper with an extended bibliography and a revised title. A brief note is added to point out a systematic way to spontaneously break Lorentz symmetr

Buneman instability in a magnetized current-carrying plasma with velocity shear

Buneman instability is often driven in magnetic reconnection. Understanding how velocity shear in the beams driving the Buneman instability affects the growth and saturation of waves is relevant to turbulence, heating, and diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak cosine velocity shear together with Vlasov simulations, the effects of shear on the kinetic Buneman instability are studied in a plasma consisting of strongly magnetized electrons and cold unmagnetized ions. In the linearly unstable phase, shear enhances the coupling between oblique waves and the sheared electron beam, resulting in a wider range of unstable eigenmodes with common lower growth rates. The wave couplings generate new features of the electric fields in space, which can persist into the nonlinear phase when electron holes form. Lower hybrid instabilities simultaneously occur at $k_{\shortparallel}/k_{\perp} \sim \sqrt{m_e/m_i}$ with a much lower growth rate, and are not affected by the velocity shear.Comment: Accepted by Physics of Plasm