Energy dissipation in wave propagation in general relativistic plasma

Based on a recent communication by the present authors the question of energy dissipation in magneto hydrodynamical waves in an inflating background in general relativity is examined. It is found that the expanding background introduces a sort of dragging force on the propagating wave such that unlike the Newtonnian case energy gets dissipated as it progresses. This loss in energy having no special relativistic analogue is, however, not mechanical in nature as in elastic wave. It is also found that the energy loss is model dependent and also depends on the number of dimensions.Comment: 12 page

An Action for Black Hole Membranes

The membrane paradigm is the remarkable view that, to an external observer, a black hole appears to behave exactly like a dynamical fluid membrane, obeying such pre-relativistic equations as Ohm's law and the Navier-Stokes equation. It has traditionally been derived by manipulating the equations of motion. Here we provide an action formulation of this picture, clarifying what underlies the paradigm, and simplifying the derivations. Within this framework, we derive previous membrane results, and extend them to dyonic black hole solutions. We discuss how it is that an action can produce dissipative equations. Using a Euclidean path integral, we show that familiar semi-classical thermodynamic properties of black holes also emerge from the membrane action. Finally, in a Hamiltonian description, we establish the validity of a minimum entropy production principle for black holes.Comment: LaTeX, 30 Pages, minor editorial change

The structure of black hole magnetospheres. I. Schwarzschild black holes

We introduce a multipolar scheme for describing the structure of stationary, axisymmetric, force-free black-hole magnetospheres in the ``3+1'' formalism. We focus here on Schwarzschild spacetime, giving a complete classification of the separable solutions of the stream equation. We show a transparent term-by-term analogy of our solutions with the familiar multipoles of flat-space electrodynamics. We discuss electrodynamic processes around disk-fed black holes in which our solutions find natural applications: (a) ``interior'' solutions in studies of the Blandford-Znajek process of extracting the hole's rotational energy, and of the formation of relativistic jets in active galactic nuclei and ``microquasars'', and, (b) ``exterior'' solutions in studies of accretion disk dynamos, disk-driven winds and jets. On the strength of existing numerical studies, we argue that the poloidal field structures found here are also expected to hold with good accuracy for rotating black holes, except for maximum possible rotation rates. We show that the closed-loop exterior solutions found here are not in contradiction with the Macdonald-Thorne theorem, since these solutions, which diverge logarithmically on the hole's horizon $\cal H$, apply only to those regions which exclude $\cal H$.Comment: 6 figures. Accepted for publication by MNRA

Thermal Control of Spin Excitations in the Coupled Ising-Chain Material RbCoCl₃

We have used neutron spectroscopy to investigate the spin dynamics of the quantum (S = 1/2) antiferromagnetic Ising chains in RbCoCl3. The structure and magnetic interactions in this material conspire to produce two magnetic phase transitions at low temperatures, presenting an ideal opportunity for thermal control of the chain environment. The high-resolution spectra we measure of two-domain-wall excitations therefore characterize precisely both the continuum response of isolated chains and the "Zeeman-ladder" bound states of chains in three different effective staggered fields in one and the same material. We apply an extended Matsubara formalism to obtain a quantitative description of the entire dataset, Monte Carlo simulations to interpret the magnetic order, and finite-temperature density-matrix renormalization-group calculations to fit the spectral features of all three phases

Znajek-Damour Horizon Boundary Conditions with Born-Infeld Electrodynamics

In this work, the interaction of electromagnetic fields with a rotating (Kerr) black hole is explored in the context of Born-Infeld (BI) theory of electromagnetism instead of standard Maxwell theory and particularly BI theory versions of the four horizon boundary conditions of Znajek and Damour are derived. Naturally, an issue to be addressed is then whether they would change from the ones given in Maxwell theory context and if they would, how. Interestingly enough, as long as one employs the same local null tetrad frame as the one adopted in the works by Damour and by Znajek to read out physical values of electromagnetic fields and fictitious surface charge and currents on the horizon, it turns out that one ends up with exactly the same four horizon boundary conditions despite the shift of the electrodynamics theory from a linear Maxwell one to a highly non-linear BI one. Close inspection reveals that this curious and unexpected result can be attributed to the fact that the concrete structure of BI equations happens to be such that it is indistinguishable at the horizon to a local observer, say, in Damour's local tetrad frame from that of standard Maxwell theory.Comment: 38 pages, Revtex, typos corrected, accepted for publication in Phys. Rev.

Scalar field and electromagnetic perturbations on Locally Rotationally Symmetric spacetimes

We study scalar field and electromagnetic perturbations on Locally Rotationally Symmetric (LRS) class II spacetimes, exploiting a recently developed covariant and gauge-invariant perturbation formalism. From the Klein-Gordon equation and Maxwell's equations, respectively, we derive covariant and gauge-invariant wave equations for the perturbation variables and thereby find the generalised Regge-Wheeler equations for these LRS class II spacetime perturbations. As illustrative examples, the results are discussed in detail for the Schwarzschild and Vaidya spacetime, and briefly for some classes of dust Universes.Comment: 22 pages; v3 has minor changes to match published versio

Region of magnetic dominance near a rotating black hole

This is a brief contribution in which a simplified criterion of the relevance of the test-particle approximation describing motion of material near a magnetized black hole is discussed. Application to processes of the dissipative collimation of astronomical jets (as proposed by de Felice and Curir, 1992) is mentioned.Comment: 11 pages, to appear in General Relativity and Gravitation, also available (with additional illustrations) at http://otokar.troja.mff.cuni.cz/user/karas/au_www/karas/papers.ht

The Stretched Horizon and Black Hole Complementarity

Three postulates asserting the validity of conventional quantum theory, semi-classical general relativity and the statistical basis for thermodynamics are introduced as a foundation for the study of black hole evolution. We explain how these postulates may be implemented in a ``stretched horizon'' or membrane description of the black hole, appropriate to a distant observer. The technical analysis is illustrated in the simplified context of 1+1 dimensional dilaton gravity. Our postulates imply that the dissipative properties of the stretched horizon arise from a course graining of microphysical degrees of freedom that the horizon must possess. A principle of black hole complementarity is advocated. The overall viewpoint is similar to that pioneered by 't~Hooft but the detailed implementation is different.Comment: (some misprints in equations have been fixed), 48 pages (including figures), SU-ITP-93-1

Evaluation of the effects of wheat gluten source and animal plasma blends on the growth performance of nursery pigs

A total of 472 weanling pigs (initially 13.5 lb) were used in two experiments to evaluate the effects of wheat gluten source (WG) and combinations with spray-dried animal plasma (SDAP) on growth performance of nursery pigs. In Exp. 1, the five dietary treatments included a control diet containing 6% SDAP, wheat gluten that was enzymatically hydrolyzed (Source 1), and a non-hydrolyzed wheat gluten (Source 2). The wheat gluten sources replaced L-lysine HCl and replaced 50% or 100% of the spray-dried animal plasma. From d 0 to 7, 7 to 14, and 0 to 21, increasing wheat gluten decreased (linear; P\u3c0.05) ADG. There were no differences between wheat gluten sources. Average daily feed intake decreased similar to ADG, with the exception that ADFI of pigs fed wheat gluten Source 2 had only a slight decreasing trend (P\u3c0.11) from d 0 to 7. Pigs fed the diet containing 6% SDAP had the greatest ADG and ADFI from d 0 to 21. When the SDAP was replaced with either wheat gluten source, ADG and ADFI linearly decreased (P\u3c0.01) but F/G improved (P\u3c0.04). When pigs were fed the common diet from d 21 to 35, there were no differences (P\u3c0.05) in ADG, ADFI or F/G. In Exp. 2, the six dietary treatments included a negative control with no SDAP or WG (0:0 ratio), 9% WG (100:0 ratio), 6.75% WG and 1.25% SDAP (75:25 ratio) combination, 4.5% WG and 2.5% SDAP (50:50 ratio) combination, 2.25% WG and 3.75% SDAP (25:75 ratio) combination, and a positive control with 5% SDAP (0:100 ratio). The wheat gluten (Source 1) was enzymatically hydrolyzed, but from a different lot than Exp. 1. From d 0 to 14, pigs fed 6% SDAP had numerically greater ADG and ADFI compared to pigs fed the negative control diet. However, replacing SDAP with increasing amounts of WG tended to decrease (P\u3c0.10) ADG and ADFI. These results confirm the improved ADG and ADFI of pigs fed SDAP immediately after weaning. In these experiments, replacing SDAP with WG resulted in decreased ADG.; Swine Day, Manhattan, KS, November 14, 200

The self-force on a static scalar test-charge outside a Schwarzschild black hole

The finite part of the self-force on a static scalar test-charge outside a Schwarzschild black hole is zero. By direct construction of Hadamard's elementary solution, we obtain a closed-form expression for the minimally coupled scalar field produced by a test-charge held fixed in Schwarzschild spacetime. Using the closed-form expression, we compute the necessary external force required to hold the charge stationary. Although the energy associated with the scalar field contributes to the renormalized mass of the particle (and thereby its weight), we find there is no additional self-force acting on the charge. This result is unlike the analogous electrostatic result, where, after a similar mass renormalization, there remains a finite repulsive self-force acting on a static electric test-charge outside a Schwarzschild black hole. We confirm our force calculation using Carter's mass-variation theorem for black holes. The primary motivation for this calculation is to develop techniques and formalism for computing all forces - dissipative and non-dissipative - acting on charges and masses moving in a black-hole spacetime. In the Appendix we recap the derivation of the closed-form electrostatic potential. We also show how the closed-form expressions for the fields are related to the infinite series solutions.Comment: RevTeX, To Appear in Phys. Rev.