Dynamics of electromagnetic waves in Kerr geometry

Here we are interested to study the spin-1 particle i.e., electro-magnetic wave in curved space-time, say around black hole. After separating the equations into radial and angular parts, writing them according to the black hole geometry, say, Kerr black hole we solve them analytically. Finally we produce complete solution of the spin-1 particles around a rotating black hole namely in Kerr geometry. Obviously there is coupling between spin of the electro-magnetic wave and that of black hole when particles propagate in that space-time. So the solution will be depending on that coupling strength. This solution may be useful to study different other problems where the analytical results are needed. Also the results may be useful in some astrophysical contexts.Comment: 15 Latex pages, 4 Figures; Accepted for publication in Classical and Quantum Gravit

Regularization of the Teukolsky Equation for Rotating Black Holes

We show that the radial Teukolsky equation (in the frequency domain) with sources that extend to infinity has well-behaved solutions. To prove that, we follow Poisson approach to regularize the non-rotating hole, and extend it to the rotating case. To do so we use the Chandrasekhar transformation among the Teukolsky and Regge-Wheeler-like equations, and express the integrals over the source in terms of solutions to the homogeneous Regge-Wheeler-like equation, to finally regularize the resulting integral. We then discuss the applicability of these results.Comment: 14 pages, 1 Table, REVTE

Fermion scattering by a Schwarzschild black hole

We study the scattering of massive spin-half waves by a Schwarzschild black hole using analytical and numerical methods. We begin by extending a recent perturbation theory calculation to next order to obtain Born series for the differential cross section and Mott polarization, valid at small couplings. We continue by deriving an approximation for glory scattering of massive spinor particles by considering classical timelike geodesics and spin precession. Next, we formulate the Dirac equation on a black hole background, and outline a simple numerical method for finding partial wave series solutions. Finally, we present our numerical calculations of absorption and scattering cross sections and polarization, and compare with theoretical expectations.Comment: Minor changes, 1 figure added. Version to appear in Phys. Rev. D. 36 pages, 13 figure

Inferring black hole charge from backscattered electromagnetic radiation

We compute the scattering cross section of Reissner-Nordström black holes for the case of an incident electromagnetic wave. We describe how scattering is affected by both the conversion of electromagnetic to gravitational radiation, and the parity dependence of phase shifts induced by the black hole charge. The latter effect creates a helicity-reversed scattering amplitude that is nonzero in the backward direction. We show that from the character of the electromagnetic wave scattered in the backward direction it is possible, in principle, to infer if a static black hole is charged

Spacetime Splitting, Admissible Coordinates and Causality

To confront relativity theory with observation, it is necessary to split spacetime into its temporal and spatial components. The (1+3) timelike threading approach involves restrictions on the gravitational potentials $(g_{\mu \nu})$, while the (3+1) spacelike slicing approach involves restrictions on $(g^{\mu \nu})$. These latter coordinate conditions protect chronology within any such coordinate patch. While the threading coordinate conditions can be naturally integrated into the structure of Lorentzian geometry and constitute the standard coordinate conditions in general relativity, this circumstance does not extend to the slicing coordinate conditions. We explore the influence of chronology violation on wave motion. In particular, we consider the propagation of radiation parallel to the rotation axis of stationary G\"odel-type universes characterized by parameters $\eta > 0$ and $\lambda > 0$ such that for $\eta 1$) chronology is protected (violated). We show that in the WKB approximation such waves can freely propagate only when chronology is protected.Comment: 25 pages, 3 figures; v2: minor typos corrected, accepted for publication in Phys. Rev.

Rainbow scattering in the gravitational field of a compact object

We study the elastic scattering of a planar wave in the curved spacetime of a compact object such as a neutron star, via a heuristic model: a scalar field impinging upon a spherically symmetric uniform density star of radius R and mass M. For R<rc, there is a divergence in the deflection function at the light-ring radius rc ¼ 3GM=c2, which leads to spiral scattering (orbiting) and a backward glory; whereas for R>rc, there instead arises a stationary point in the deflection function which creates a caustic and rainbow scattering. As in nuclear rainbow scattering, there is an Airy-type oscillation on a Rutherford-like cross section, followed by a shadow zone. We show that, for R ∼ 3.5GM=c2, the rainbow angle lies close to 180°, and thus there arises enhanced backscattering and glory. We explore possible implications for gravitational wave astronomy and dark matter models

Gravitational Couplings of Intrinsic Spin

The gravitational couplings of intrinsic spin are briefly reviewed. A consequence of the Dirac equation in the exterior gravitational field of a rotating mass is considered in detail, namely, the difference in the energy of a spin-1/2 particle polarized vertically up and down near the surface of a rotating body is $\hbar\Omega\sin\theta$. Here $\theta$ is the latitude and $\Omega = 2GJ/(c^2 R^3)$, where $J$ and $R$ are, respectively, the angular momentum and radius of the body. It seems that this relativistic quantum gravitational effect could be measurable in the foreseeable future.Comment: LaTeX file, no figures, 16 page

Grand Challenges: Improving HIV Treatment Outcomes by Integrating Interventions for Co-Morbid Mental Illness.

In the fourth article of a five-part series providing a global perspective on integrating mental health, Sylvia Kaaya and colleagues discuss the importance of integrating mental health interventions into HIV prevention and treatment platforms. Please see later in the article for the Editors' Summary

Strategies to facilitate integrated care for people with alcohol and other drug problems: a systematic review

Background: There is a growing body of research highlighting the potential benefits of integrated care as a way of addressing the needs of people with alcohol and other drug (AOD) problems, given the broad range of other issues clients often experience. However, there has been little academic attention on the strategies that treatment systems, agencies and clinicians could implement to facilitate integrated care. Methods: We synthesised the existing evidence on strategies to improve integrated care in an AOD treatment context by conducting a systematic review of the literature. We searched major academic databases for peer-reviewed articles that evaluated strategies that contribute to integrated care in an AOD context between 1990 and 2014. Over 2600 articles were identified, of which 14 met the study inclusion criteria of reporting on an empirical study to evaluate the implementation of integrated care strategies. The types of strategies utilised in included articles were then synthesised. Results: We identified a number of interconnected strategies at the funding, organisational, service delivery and clinical levels. Ensuring that integrated care is included within service specifications of commissioning bodies and is adequately funded was found to be critical in effective integration. Cultivating positive inter-agency relationships underpinned and enabled the implementation of most strategies identified. Staff training in identifying and responding to needs beyond clinicians' primary area of expertise was considered important at a service level. However, some studies highlight the need to move beyond discrete training events and towards longer term coaching-type activities focussed on implementation and capacity building. Sharing of client information (subject to informed consent) was critical for most integrated care strategies. Case-management was found to be a particularly good approach to responding to the needs of clients with multiple and complex needs. At the clinical level, screening in areas beyond a clinician's primary area of practice was a common strategy for facilitating referral and integrated care, as was joint care planning. Conclusion: Despite considerable limitations and gaps in the literature in terms of the evaluation of integrated care strategies, particularly between AOD services, our review highlights several strategies that could be useful at multiple levels. Given the interconnectedness of integrated care strategies identified, implementation of multi-level strategies rather than single strategies is likely to be preferable

Mamekhaya: a pilot study combining a cognitive-behavioral intervention and mentor mothers with PMTCT services in South Africa

Nearly 30% of pregnant women in South Africa are estimated to be HIV seropositive, yet adherence to guidelines for the prevention of mother-to-child transmission of HIV (PMTCT) is often low. A pilot study was developed to see whether PMTCT services provided by the South African Government could be enhanced by the Mamekhaya program, a combination of the mothers2mothers peer-mentoring program and a culturally adapted cognitive-behavioral intervention (CBI) from the USA. Pregnant women attending two maternity clinics offering PMTCT in Gugulethu and Vanguard Townships, Cape Town, South Africa, were invited to participate in the study. Women at the intervention site (Gugulethu) received the support of a mentor mother and also attended an eight-session Mamekhaya CBI. At the control site (Vanguard), women received standard services provided by midwives and counselors. Baseline assessments were completed by all participants at enrollment (n=160), and follow-ups were completed six months later by 44% of participants. Self-reports of adherence to PMTCT practices were high across both sites (90% or more engaging in the core practices). Women at the Mamekhaya site showed significantly greater improvement in establishing social support and reducing depression scores than women at the control site. Mamekhaya participants also showed trends for better attendance at follow-up medical visits, and greater improvements in positive coping. The greatest effect of the Mamekhaya program was to increase HIV knowledge scores, particularly with regard to understanding the meaning and importance of viral load and CD4 test results. Results from this pilot study show promise that augmenting basic PMTCT services with mentor mothers and a culturally adapted CBI can be effective in conveying information and in improving the emotional outlook and hopefulness of HIV-positive pregnant women in South Africa