Field theory of the photon self-energy in a medium with a magnetic field and the Faraday effect

A convenient and general decomposition of the photon self-energy in a magnetized, but otherwise isotropic, medium is given in terms of the minimal set of tensors consistent with the transversality condition. As we show, the self-energy in such a medium is completely parametrized in terms of nine independent form factors, and they reduce to three in the long wavelength limit. We consider in detail an electron gas with a background magnetic field, and using finite temperature field theory methods, we obtain the one-loop formulas for the form factors, which are exact to all orders in the magnetic field. Explicit results are derived for a variety of physical conditions. In the appropriate limits, we recover the well-known semi-classical results for the photon dispersion relations and the Faraday effect. In more general cases, where the semi-classical treatment or the linear approximation (weak field limit) are not applicable, our formulas provide a consistent and systematic way for computing the self-energy form factors and, from them, the photon dispersion relations.Comment: Revtex, 27 page

Faraday effect : a field theoretical point of view

We analyze the structure of the vacuum polarization tensor in the presence of a background electromagnetic field in a medium. We use various discrete symmetries and crossing symmetry to constrain the form factors obtained for the most general case. From these symmetry arguments, we show why the vacuum polarization tensor has to be even in the background field when there is no background medium. Taking then the background field to be purely magnetic, we evaluate the vacuum polarization to linear order in it. The result shows the phenomenon of Faraday rotation, i.e., the rotation of the plane of polarization of a plane polarized light passing through this background. We find that the usual expression for Faraday rotation, which is derived for a non-degenerate plasma in the non-relativistic approximation, undergoes substantial modification if the background is degenerate and/or relativistic. We give explicit expressions for Faraday rotation in completely degenerate and ultra-relativistic media.Comment: 20 pages, Latex, uses axodraw.st

Constraining Sources of Ultra High Energy Cosmic Rays Using High Energy Observations with the Fermi Satellite

We analyze the conditions that enable acceleration of particles to ultra-high energies, ~10^{20} eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the ability of active galactic nuclei (AGN) to produce UHECRs. The high energy (MeV - GeV) photons are produced by Compton scattering of the emitted low energy photons and the cosmic microwave background or extra-galactic background light. The ratio of the luminosities at high and low photon energies can therefore be used as a probe of the physical conditions in the acceleration site. We find that existing data excludes core regions of nearby radio-loud AGN as possible acceleration sites of UHECR protons. However, we show that giant radio lobes are not excluded. We apply our method to Cen A, and show that acceleration of protons to ~10^{20} eV can only occur at distances >~ 100 kpc from the core.Comment: Extended discussion on former results; Accepted for publication in JCA

Menus for Feeding Black Holes

Black holes are the ultimate prisons of the Universe, regions of spacetime where the enormous gravity prohibits matter or even light to escape to infinity. Yet, matter falling toward the black holes may shine spectacularly, generating the strongest source of radiation. These sources provide us with astrophysical laboratories of extreme physical conditions that cannot be realized on Earth. This chapter offers a review of the basic menus for feeding matter onto black holes and discusses their observational implications.Comment: 27 pages. Accepted for publication in Space Science Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher

Supermassive Black Hole Binaries: The Search Continues

Gravitationally bound supermassive black hole binaries (SBHBs) are thought to be a natural product of galactic mergers and growth of the large scale structure in the universe. They however remain observationally elusive, thus raising a question about characteristic observational signatures associated with these systems. In this conference proceeding I discuss current theoretical understanding and latest advances and prospects in observational searches for SBHBs.Comment: 17 pages, 4 figures. To appear in the Proceedings of 2014 Sant Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed. C.Sopuerta (Berlin: Springer-Verlag

Observations and models to support the first Marine Ecosystem Assessment for the Southern Ocean (MEASO)

Assessments of the status and trends of habitats, species and ecosystems are needed for effective ecosystem-based management in marine ecosystems. Knowledge on imminent ecosystem changes (climate change impacts) set in train by existing climate forcings are needed for adapting management practices to achieve conservation and sustainabililty targets into the future. Here, we describe a process for enabling a marine ecosystem assessment (MEA) by the broader scientific community to support managers in this way, using a MEA for the Southern Ocean (MEASO) as an example. We develop a framework and undertake an audit to support a MEASO, involving three parts. First, we review available syntheses and assessments of the Southern Ocean ecosystem and its parts, paying special attention to building on the SCAR Antarctic Climate Change and Environment report and the SCAR Biogeographic Atlas of the Southern Ocean. Second, we audit available field observations of habitats and densities and/or abundances of taxa, using the literature as well as a survey of scientists as to their current and recent activities. Third, we audit available system models that can form a nested ensemble for making, with available data, circumpolar assessments of habitats, species and food webs. We conclude that there is sufficient data and models to undertake, at least, a circumpolar assessment of the krill-based system. The auditing framework provides the basis for the first MEASO but also provides a repository (www.SOKI.aq/display/MEASO) for easily amending the audit for future MEASOs. We note that an important outcome of the first MEASO will not only be the assessment but also to advise on priorities in observations and models for improving subsequent MEASOs

A multi-center study on the attitudes of Malaysian emergency health care staff towards allowing family presence during resuscitation of adult patients

BACKGROUND The practice of allowing family members to witness on-going active resuscitation has been gaining ground in many developed countries since it was first introduced in the early 1990s. In many Asian countries, the acceptability of this practice has not been well studied. AIM We conducted a multi-center questionnaire study to determine the attitudes of health care professionals in Malaysia towards family presence to witness ongoing medical procedures during resuscitation. METHODS Using a bilingual questionnaire (in Malay and English language), we asked our respondents about their attitudes towards allowing family presence (FP) as well as their actual experience of requests from families to be allowed to witness resuscitations. Multiple logistic regression was used to analyze the association between the many variables and a positive attitude towards FP. RESULTS Out of 300 health care professionals who received forms, 270 responded (a 90% response rate). Generally only 15.8% of our respondents agreed to allow relatives to witness resuscitations, although more than twice the number (38.5%) agreed that relatives do have a right to be around during resuscitation. Health care providers are significantly more likely to allow FP if the procedures are perceived as likely to be successful (e.g., intravenous cannulation and blood taking as compared to chest tube insertion). Doctors were more than twice as likely as paramedics to agree to FP (p-value = 0.002). This is probably due to the Malaysian work culture in our health care systems in which paramedics usually adopt a 'follow-the-leader' attitude in their daily practice. CONCLUSION The concept of allowing FP is not well accepted among our Malaysian health care providers

Introductie van soorten via maaisel na herinrichting: Ongeduld of wijsheid?

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