Astrophysical signatures of boson stars: quasinormal modes and inspiral resonances

Compact bosonic field configurations, or boson stars, are promising dark matter candidates which have been invoked as an alternative description for the supermassive compact objects in active galactic nuclei. Boson stars can be comparable in size and mass to supermassive black holes and they are hard to distinguish by electromagnetic observations. However, boson stars do not possess an event horizon and their global spacetime structure is different from that of a black hole. This leaves a characteristic imprint in the gravitational-wave emission, which can be used as a discriminant between black holes and other horizonless compact objects. Here we perform a detailed study of boson stars and their gravitational-wave signatures in a fully relativistic setting, a study which was lacking in the existing literature in many respects. We construct several fully relativistic boson star configurations, and we analyze their geodesic structure and free oscillation spectra, or quasinormal modes. We explore the gravitational and scalar response of boson star spacetimes to an inspiralling stellar-mass object and compare it to its black hole counterpart. We find that a generic signature of compact boson stars is the resonant-mode excitation by a small compact object on stable quasi-circular geodesic motion.Comment: 20 pages, 8 figures. v2: minor corrections, version to be published in Phys. Rev. D. v3: final versio

Slowly Rotating Anisotropic Neutron Stars in General Relativity and Scalar-Tensor Theory

Some models (such as the Skyrme model, a low-energy effective field theory for QCD) suggest that the high-density matter prevailing in neutron star interiors may be significantly anisotropic. Anisotropy is known to affect the bulk properties of nonrotating neutron stars in General Relativity. In this paper we study the effects of anisotropy on slowly rotating stars in General Relativity. We also consider one of the most popular extensions of Einstein's theory, namely scalar-tensor theories allowing for spontaneous scalarization (a phase transition similar to spontaneous magnetization in ferromagnetic materials). Anisotropy affects the moment of inertia of neutron stars (a quantity that could potentially be measured in binary pulsar systems) in both theories. We find that the effects of scalarization increase (decrease) when the tangential pressure is bigger (smaller) than the radial pressure, and we present a simple criterion to determine the onset of scalarization by linearizing the scalar-field equation. Our calculations suggest that binary pulsar observations may constrain the degree of anisotropy or even, more optimistically, provide evidence for anisotropy in neutron star cores.Comment: 19 pages, 7 figures, 1 table. Matches version in press in CQG. Fixed small typo

The process of agricultural technology generation in Brazil: a social audit.

The focus of agricultural technology studies in Brazil has been on technology diffusion or adoption. This approach stresses the neutrality of technology and its adoption depends on farmers' psychological and individual values. The agricultural technology generation process and the organisations in which technology is generated have not been considered as active factors. This thesis regards both as highly significant in farmers' adoption or rejection of technology. Approaches to development, modernisation and underdevelopment, along with agricultural globalisation, are the applied theoretical perspectives used to understand what happens in the underdeveloped countries in an integrated world system. This is an ex-post facto and cross-sectional study. The empirical data, based on a case study, was collected in Brazil, in and around the Brazilian Agricultural Research Organisation (EMBRAPA), a topdown state-owned organisation. Agricultural technology generation, its adoption, as well as the attitudes of users, clients, policy-makers, politicians and unions to the agricultural technology generation process were investigated. The fieldwork was conducted with eighty-seven agricultural researchers from four national agricultural research centres, one hundred and forty-four farmers, and eighty individuals and organisations' representatives. Qualitative and quantitative analyses indicated that the agricultural technology generation process is related more to scientific issues than to farmers' demands. The technology adopted by farmers was determined primarily by developments within the process of technology generation rather than through any persuasion. The thesis concludes that as a result of the process of technology generation in EMBRAP A, organised and capitalist farmers have been targeted rather than small or subsistence farmers. Therefore, the new farm as a whole research model is recommended, which explores the whole production system rather than specific agricultural products.Dissertation (Doctor in Philosophy)- School of Social Sciences, University of Sussex. Tese de doutorado

Isotretinoin and inflammatory bowel disease

[Excerpt] We read with great interest the recent review published in your Journal by Reddy et al., which suggests a possible association between isotretinoin use and inflammatory bowel disease (IBD) (1). Although IBD is described as a possible adverse drug reaction in the product information, little attention has been given in the literature to this association.[...

Relation between BCG coverage rate and COVID-19 infection worldwide

The available numbers on COVID-19 have shown a huge difference in incidence rates worldwide [1]. The explanation for these differences is certainly multifactorial and more time is needed for accurate data analysis and to a complete understanding.info:eu-repo/semantics/publishedVersio