Semiclassical approach to black hole absorption of electromagnetic radiation emitted by a rotating charge

We consider an electric charge, minimally coupled to the Maxwell field, rotating around a Schwarzschild black hole. We investigate how much of the radiation emitted from the swirling charge is absorbed by the black hole and show that most of the photons escape to infinity. For this purpose we use the Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman gauge developed in the context of quantum field theory in Schwarzschild spacetime. We obtain that the two photon polarizations contribute quite differently to the emitted power. In addition, we discuss the accurateness of the results obtained in a full general relativistic approach in comparison with the ones obtained when the electric charge is assumed to be orbiting a massive object due to a Newtonian force.

Interaction of Hawking radiation with static sources in de Sitter and Schwarzschild-de Sitter spacetimes

We study and look for similarities between the response rates R-dS(a(0),Lambda) and R-SdS(a(0),Lambda,M) of a static scalar source with constant proper acceleration a(0) interacting with a massless, conformally coupled Klein-Gordon field (i) in de Sitter spacetime, in the Euclidean vacuum, which describes a thermal flux of radiation emanating from the de Sitter cosmological horizon and (ii) in Schwarzschild-de Sitter spacetime, in the Gibbons-Hawking vacuum, which describes thermal fluxes of radiation emanating from both the hole and the cosmological horizons, respectively, where Lambda is the cosmological constant and M is the black hole mass. After performing the field quantization in each of the above spacetimes, we obtain the response rates at the tree level in terms of an infinite sum of zero-energy field modes possessing all possible angular momentum quantum numbers. In the case of de Sitter spacetime, this formula is worked out and a closed, analytical form is obtained. In the case of Schwarzschild-de Sitter spacetime such a closed formula could not be obtained, and a numerical analysis is performed. We conclude, in particular, that R-dS(a(0),Lambda) and R-SdS(a(0),Lambda,M) do not coincide in general, but tend to each other when Lambda-->0 or a(0)-->infinity. Our results are also contrasted and shown to agree (in the proper limits) with related ones in the literature.

Scaler radiation emitted from a source rotating around a black hole

We analyse the scalar radiation emitted from a source rotating around a Schwarzschild black hole using the framework of quantum held theory at the tree level. We show that for relativistic circular orbits the emitted power is about 20-30% smaller than what would be obtained in Minkowski spacetime. We also show that most of the emitted energy escapes to infinity. Our formalism can readily be adapted to investigate similar processes.

Sum rules in the oscillator radiation processes

We consider the problem of a harmonic oscillator coupled to a scalar field in the framework of recently introduced dressed coordinates. We compute all the probabilities associated with the decay process of an excited level of the oscillator. Instead of doing direct quantum mechanical calculations we establish some sum rules from which we infer the probabilities associated to the different decay processes of the oscillator. Thus, the sum rules allows to show that the transition probabilities between excited levels follow a binomial distribution. (c) 2005 Published by Elsevier B.V.

THERMAL RADIATION FROM A FLUCTUATING EVENT HORIZON

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

First study of the radiation-amplitude zero in W gamma production and limits on anomalous WW gamma couplings at root s=1.96 TeV

We present results from a study of p (p) over bar -> W gamma+X events utilizing data corresponding to 0.7 fb(-1) of integrated luminosity at root s = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WW gamma couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49 radiation-amplitude zero in the W gamma system.

Scalar radiation emitted from a rotating source around a Reissner-Nordstrom black hole

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Radiation interference from sources rotating around Schwarzschild black holes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Radionuclide concentrations in raw and purified phosphoric acids from Brazil and their processing wastes: implications for radiation exposures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The interaction between atoms of Au and Cu with clean Si(111) surface: A study combining synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Refractive index changes in photochromic SbPO4-WO3 glass by exposure to band-gap radiation

We report photoinduced photo-darkening in SbPO4-WO3 glass by exposure to 532 nm light with a power density of 143 mW/cm(2). The time of exposure was varied between 0 and 256 min following which visible photo-darkening, peaking at 850 nm was observed. Spectrophotometer measurement of absorption was performed for both treated and untreated regions of the sample. Time exposure to below band-gap light results in a single exponent Gaussian absorption function over an exceptionally wide range of wavelengths (500 nm-1600 nm), with a 1/e width of 647.5 nm. Kramers-Kronig transform of the change in the absorption indicates a negative local change in the refractive index. The dispersed refractive index change at 1550 nm, Delta n, is calculated to be similar to -5 x 10(-8). The peak absorption increases with time of exposure and the photo-darkening remains irreversible at room temperature. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Effects of 60Co gamma radiation on crotamine

Ionizing radiation can change the molecular structure and affect the biological properties of biomolecules. This has been employed to attenuate animal toxins. Crotamine is a strongly basic polypeptide (pI 10.3) from Crotalus durissus terrificus venom composed of 42 amino acid residues. It induces skeletal muscle spasms leading to a spastic paralysis of hind limbs in mice. The objective of the present study was to carry out a biochemical study and a toxic activity assay on native and irradiated crotamine. Crotamine was purified from C.d. terrificus venom by Sephadex G-100 gel filtration followed by ion-exchange chromatography, and irradiated at 2 mg/ml in 0.15 M NaCl with 2.0 kGy gamma radiation emitted by a 60Co source. The native and irradiated toxins were evaluated in terms of structure and toxic activity (LD50). Irradiation did not change the protein concentration, the electrophoretic profile or the primary structure of the protein although differences were shown by spectroscopic techniques. Gamma radiation reduced crotamine toxicity by 48.3%, but did not eliminate it.

Growth and physiological responses of sunflower plants exposed to ultraviolet-B radiation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)