136 research outputs found
On the Polarized Absorption Lines in Gamma-Ray Burst Optical Afterglows
Spectropolarimetric measurements of gamma-ray burst (GRB) optical afterglows contain polarization information for both continuum and absorption lines. Based on the Zeeman effect, an absorption line in a strong magnetic field is polarized and split into a triplet. In this paper, we solve the polarization radiative transfer equations of the absorption lines, and obtain the degree of linear polarization of the absorption lines as a function of the optical depth. In order to effectively measure the degree of linear polarization for the absorption lines, a magnetic field strength of at least 103 G is required. The metal elements that produce the polarized absorption lines should be sufficiently abundant and have large oscillation strengths or Einstein absorption coefficients. We encourage both polarization measurements and high-dispersion observations of the absorption lines in order to detect the triplet structure in early GRB optical afterglows
Brecht e Boal: Imagens tomando posição
O artigo analisa pontos e desencontros entre Brecht e Boal a partir da anĂĄlise que Didi-Hubermn apresenta no livro âCuando las imagĂ©nes toman posiciĂłnâ. Aborda como a imagem foi mostrada a partir do Holocausto e suas interpretaçÔes e possĂveis alternativas para a continuidade de um trabalho crĂtico sobre a imagem. Tendo como referĂȘncia para essa anĂĄlise uma comparação com a proposta de Brecht do seu trabalho âfoto-jornalistĂcoâ do ABC da Guerra e o Teatro-Jornal, umas das tĂ©cnicas do Teatro do Oprimido, criada em 1971, e suas novas experiĂȘncias no sĂ©culo XXI realizadas pelo Centro de Teatro do Oprimido
On the Integrand-Reduction Method for Two-Loop Scattering Amplitudes
We propose a first implementation of the integrand-reduction method for
two-loop scattering amplitudes. We show that the residues of the amplitudes on
multi-particle cuts are polynomials in the irreducible scalar products
involving the loop momenta, and that the reduction of the amplitudes in terms
of master integrals can be realized through polynomial fitting of the
integrand, without any apriori knowledge of the integral basis. We discuss how
the polynomial shapes of the residues determine the basis of master integrals
appearing in the final result. We present a four-dimensional constructive
algorithm that we apply to planar and non-planar contributions to the 4- and
5-point MHV amplitudes in N=4 SYM. The technique hereby discussed extends the
well-established analogous method holding for one-loop amplitudes, and can be
considered a preliminary study towards the systematic reduction at the
integrand-level of two-loop amplitudes in any gauge theory, suitable for their
automated semianalytic evaluation.Comment: 26 pages, 11 figure
Note on New KLT relations
In this short note, we present two results about KLT relations discussed in
recent several papers. Our first result is the re-derivation of Mason-Skinner
MHV amplitude by applying the S_{n-3} permutation symmetric KLT relations
directly to MHV amplitude. Our second result is the equivalence proof of the
newly discovered S_{n-2} permutation symmetric KLT relations and the well-known
S_{n-3} permutation symmetric KLT relations. Although both formulas have been
shown to be correct by BCFW recursion relations, our result is the first direct
check using the regularized definition of the new formula.Comment: 15 Pages; v2: minor correction
Ecological study of socio-economic indicators and prevalence of asthma in schoolchildren in urban Brazil
BACKGROUND: There is evidence of higher prevalence of asthma in populations of lower socio-economic status in affluent societies, and the prevalence of asthma is also very high in some Latin American countries, where societies are characterized by a marked inequality in wealth. This study aimed to examine the relationship between estimates of asthma prevalence based on surveys conducted in children in Brazilian cities and health and socioeconomic indicators measured at the population level in the same cities. METHODS: We searched the literature in the medical databases and in the annals of scientific meeting, retrieving population-based surveys of asthma that were conducted in Brazil using the methodology defined by the International Study of Asthma and Allergies in Childhood. We performed separate analyses for the age groups 6-7 years and 13-14 years. We examined the association between asthma prevalence rates and eleven health and socio-economic indicators by visual inspection and using linear regression models weighed by the inverse of the variance of each survey. RESULTS: Six health and socioeconomic variables showed a clear pattern of association with asthma. The prevalence of asthma increased with poorer sanitation and with higher infant mortality at birth and at survey year, GINI index and external mortality. In contrast, asthma prevalence decreased with higher illiteracy rates. CONCLUSION: The prevalence of asthma in urban areas of Brazil, a middle income country, appears to be higher in cities with more marked poverty or inequality
Analytic two-loop form factors in N=4 SYM
The original publication is available at www.springerlink.co
Evaluation of the ELISA-F29 test as an early marker of therapeutic efficacy in adults with chronic Chagas disease
Higher-Spin Interactions: four-point functions and beyond
In this work we construct an infinite class of four-point functions for
massless higher-spin fields in flat space that are consistent with the gauge
symmetry. In the Lagrangian picture, these reflect themselves in a peculiar
non-local nature of the corresponding non-abelian higher-spin couplings implied
by the Noether procedure that starts from the fourth order. We also comment on
the nature of the colored spin-2 excitation present both in the open string
spectrum and in the Vasiliev system, highlighting how some aspects of String
Theory appear to reflect key properties of Field Theory that go beyond its low
energy limit. A generalization of these results to n-point functions, fermions
and mixed-symmetry fields is also addressed.Comment: 66 pages, 10 figures, 1 table, LaTex. Several statements clarified.
Final version to appear in JHE
Spectropolarimetry and photometry of the early afterglow of the gamma-ray burst GRB191221B
We report on results of spectropolarimetry of the afterglow of the long gamma-ray burst GRB 191221B, obtained with SALT/RSS and VLT/FORS2, as well as photometry from two telescopes in the MASTER Global Robotic Network, at the MASTER-SAAO (South Africa) and MASTER-OAFA (Argentina) stations. Prompt optical emission was detected by MASTER-SAAO 38 s after the alert, which dimmed from a magnitude (white-light) of ~10 to 16.2 mag over a period of ~10 ks, followed by a plateau phase lasting ~10 ks and then a decline to ~18 mag after 80 ks. The light curve shows complex structure, with four or five distinct breaks in the power-law decline rate. SALT/RSS linear spectropolarimetry of the afterglow began ~2.9 h after the burst, during the early part of the plateau phase of the light curve. Absorption lines seen at ~6010 \r{A} and 5490 \r{A} are identified with the Mg II 2799 \r{A} line from the host galaxy at z=1.15 and an intervening system located at z=0.96. The mean linear polarisation measured over 3400-8000 \r{A} was ~1.5% and the mean equatorial position angle theta ~65 degrees. VLT/FORS2 spectropolarimetry was obtained ~10 h post-burst, during a period of slow decline (alpha = -0.44), and the polarisation was measured to be p = 1.2% and theta = 60 degrees. Two observations with the MeerKAT radio telescope, taken 30 and 444 days after the GRB trigger, detected radio emission from the host galaxy only. We interpret the light curve and polarisation of this long GRB in terms of a slow-cooling forward-shock
Asma e função pulmonar aos 6-7 anos de idade em uma coorte de nascimentos no Sul do Brasil
- âŠ