Institute Astronomia

São Paulo, Brazil

Institute Astronomia

São Paulo, Brazil
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Guimaraes K.S.F.F.,Institute Astronomia | Lourenco O.,Federal University of São Carlos | De Paula W.,Instituto Tecnologico Of Aeronutica | Frederico T.,Instituto Tecnologico Of Aeronutica | Dos Reis A.C.,Brazilian Center for Research in Physics (CBPF)
Journal of High Energy Physics | Year: 2014

The final state interaction contribution to D + decays is computed for the K - π + π + channel within a light-front relativistic three-body model for the final state interaction. The rescattering process between the kaon and two pions in the decay channel is considered. The off-shell decay amplitude is a solution of a four-dimensional Bethe-Salpeter equation, which is decomposed in a Faddeev form. The projection onto the light-front of the coupled set of integral equations is performed via a quasi-potential approach. The S-wave Kπ interaction is introduced in the resonant isospin 1/2 and the non-resonant isospin 3/2 channels. The numerical solution of the light-front tridimensional inhomogeneous integral equations for the Faddeev components of the decay amplitude is performed perturbatively. The loop-expansion converges fast, and the three-loop contribution can be neglected in respect to the two-loop results for the practical application. The dependence on the model parameters in respect to the input amplitude at the partonic level is exploited and the phase found in the experimental analysis, is fitted with an appropriate choice of the real weights of the isospin components of the partonic amplitude. The data suggests a small mixture of total isospin 5/2 to the dominant 3/2 one. The modulus of the unsymmetrized decay amplitude, which presents a deep valley and a following increase for Kπ masses above 1.5 GeV, is fairly reproduced. This suggests the assignment of the quantum numbers 0+ to the isospin 1/2 K *(1630) resonance. © 2014 The Author(s).

Eiroa E.F.,Institute Astronomia | Simeone C.,CONICET
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We study circular shells in a (2+1)-dimensional background within the framework of Einstein-Born-Infeld theory. For shells around black holes we analyze the mechanical stability under perturbations preserving the symmetry. Shells around vacuum are also discussed. We find a large range in the values of the parameters compatible with stable configurations. © 2013 American Physical Society.

Ueda Y.,Kyoto University | Akiyama M.,Tohoku University | Hasinger G.,Institute for Astronomy | Miyaji T.,National Autonomous University of Mexico | And 3 more authors.
Astrophysical Journal | Year: 2014

We present the most up to date X-ray luminosity function (XLF) and absorption function of active galactic nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5-2 keV) and/or hard (>2 keV) band. We utilize a maximum likelihood method to reproduce the count rate versus redshift distribution for each survey, by taking into account the evolution of the absorbed fraction, the contribution from Compton-thick (CTK) AGNs, and broadband spectra of AGNs, including reflection components from tori based on the luminosity-and redshift-dependent unified scheme. We find that the shape of the XLF at z ∼ 1-3 is significantly different from that in the local universe, for which the luminosity-dependent density evolution model gives much better description than the luminosity and density evolution model. These results establish the standard population synthesis model of the X-ray background (XRB), which well reproduces the source counts, the observed fractions of CTK AGNs, and the spectrum of the hard XRB. The number ratio of CTK AGNs to the absorbed Compton-thin (CTN) AGNs is constrained to be ≈0.5-1.6 to produce the 20-50 keV XRB intensity within present uncertainties, by assuming that they follow the same evolution as CTN AGNs. The growth history of supermassive black holes is discussed based on the new AGN bolometric luminosity function. © 2014. The American Astronomical Society. All rights reserved.

Garcia-Jerez A.,University of Almeria | Luzon F.,University of Almeria | Navarro M.,University of Almeria | Santoyo M.A.,Institute Astronomia
Bulletin of the Seismological Society of America | Year: 2010

The single circular array (SCA) method is a spatial autocorrelation (SPAC)-like technique for ambient noise exploration. Its main feature is the possibility of calculation of Love-wave dispersion curves by using centerless circular arrays of 3-component seismometers, allowing independent processing of each circle. Situations in which Rayleigh-wave and Love-wave arrivals or waves coming from different azimuths are mutually correlated are also correctly dealt with in this method. An algorithm for practical calculation of the SCA coefficient B is described. The algorithm includes averaging over a set of time windows and minimizes the number of spectral ratios to be computed for the purposes of stability. Numerical tests show that SCA coefficients estimated in this way have quite a robust behavior. Bias due to use of a finite number of sensors, as well as to effects of nonpropagating incoherent noise, has been theoretically studied in both the deterministic and the stationary random-field formulations. Using a finite number of stations is a cause of bias even under isotropic illumination conditions. Nevertheless, its effect can be neglected for wavelengths-to-radius ratios above a threshold that depends on the number of evenly distributed sensors. By contrast, uncorrelated noise may affect the whole frequency band and is behind the limitations of the method at low frequencies. Finally, we present the first real data test of this method, consisting of a comparison between theoretical and experimental Love-wave dispersion curves for a site where the structure is known. In practice, the minimum wavelength for direct velocity retrieval for a pentagonal array with radius r was approximately Amin ~ 3r, although this value depends on the signal-to-noise ratio. Experiments demonstrate that the usable range can be extended, mainly toward shorter wavelengths, if the effects of noise and of the finite number of sensors are included in the analysis.

Paulucci L.,Federal University of ABC | Ferrer E.J.,University of Texas at El Paso | Horvath J.E.,Institute Astronomia | De La Incera V.,University of Texas at El Paso
Journal of Physics G: Nuclear and Particle Physics | Year: 2013

We compare the mass-radius relationship of strange stars obtained in two theoretical frameworks describing the colour-flavour-locking state of dense quark matter: the semi-empirical MIT bag model and a self-consistent approach using the Nambu-Jona-Lasinio (NJL) model. In the simplest MIT model extended to include pairing, one can make the equation of state stiffer by increasing the gap parameter so that larger maximum masses for these objects can be reached. In the NJL model, however, such an effect is not possible. To increase the gap parameter within the NJL model to values comparable to those considered in the MIT case, a noticeable increase of the diquark-coupling-constant strength is needed, but this in turn softens the equation of state producing a lower maximum star mass. This behaviour is interpreted as signalling the system crossover at high diquark coupling from a Bardeen-Cooper-Schrieffer regime to a Bose-Einstein condensate one, a process that cannot be reproduced within the simple MIT prescription. © 2013 IOP Publishing Ltd.

Paulucci L.,Federal University of ABC | Horvath J.E.,Institute Astronomia
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

The conjecture of Bodmer-Witten-Terazawa suggesting a form of quark matter (Strange Quark Matter) as the ground state of hadronic interactions has been studied in laboratory and astrophysical contexts by a large number of authors. If strange stars exist, some violent events involving these compact objects, such as mergers and even their formation process, might eject some strange matter into the interstellar medium that could be detected as a trace signal in the cosmic ray flux. To evaluate this possibility, it is necessary to understand how this matter in bulk would fragment in the form of strangelets (small lumps of strange quark matter in which finite effects become important). We calculate the mass distribution outcome using the statistical multifragmentation model and point out several caveats affecting it. In particular, the possibility that strangelets fragmentation will render a tiny fraction of contamination in the cosmic ray flux is discussed. © 2014 The Authors.

Raphaldini B.,Institute Astronomia | Raupp C.F.M.,Institute Astronomia
Astrophysical Journal | Year: 2015

The solar dynamo is known to be associated with several periodicities, with the nearly 11/22 yr cycle being the most pronounced one. Even though these quasiperiodic variations of solar activity have been attributed to the underlying dynamo action in the Sun's interior, a fundamental theoretical description of these cycles is still elusive. Here, we present a new possible direction in understanding the Sun's cycles based on resonant nonlinear interactions among magnetohydrodynamic (MHD) Rossby waves. The WKB theory for dispersive waves is applied to magnetohydrodynamic shallow-water equations describing the dynamics of the solar tachocline, and the reduced dynamics of a resonant triad composed of MHD Rossby waves embedded in constant toroidal magnetic field is analyzed. In the conservative case, the wave amplitudes evolve periodically in time, with periods on the order of the dominant solar activity timescale (∼11 yr). In addition, the presence of linear forcings representative of either convection or instabilities of meridionally varying background states appears to be crucial in balancing dissipation and thus sustaining the periodic oscillations of wave amplitudes associated with resonant triad interactions. Examination of the linear theory of MHD Rossby waves embedded in a latitudinally varying mean flow demonstrates that MHD Rossby waves propagate toward the equator in a waveguide from -35° to 35° in latitude, showing a remarkable resemblance to the structure of the butterfly diagram of the solar activity. Therefore, we argue that resonant nonlinear magnetohydrodynamic Rossby wave interactions might significantly contribute to the observed cycles of magnetic solar activity. © 2015. The American Astronomical Society. All rights reserved.

Horvath J.E.,Institute Astronomia | Galante D.,Institute Astronomia
International Journal of Astrobiology | Year: 2012

With the possible exception of meteor impacts, high-energy astrophysical events such as supernovae, gamma-ray bursts (GRB) and flares are usually not taken into account for biological and evolutionary studies due to their low rates of occurrence. We show that a class of these events may occur at distances and time scales in which their biological effects are non-negligible, maybe more frequent than the impacts of large asteroids.We review the effects of four transient astrophysical sources of ionizing radiation on biospheres - stellar flares, giant flares fromsoft gamma repeaters (SGR), supernovae and GRB. The main damaging features of them are briefly discussed and illustrated. We point out some open problems and ongoing work. Copyright © Cambridge University Press 2012.

Horvath J.E.,Institute Astronomia
International Journal of Modern Physics D | Year: 2010

We discuss the propagation of the hypothetical "combustion" n → SQM in a dense stellar environment. We address the instabilities affecting the flame and a present new results of application to the turbulent regime. The acceleration of the flame, the possible transition to the distributed regime and a further deflagration-to-detonation mechanism are addressed. As a general result, we conclude that the burning happens in (at least) either the turbulent RayleighTaylor or the distributed regime, but not in the laminar regime. In both cases the velocity of the conversion of the star is several orders of magnitude larger than ulam, making the latter irrelevant in practice for this problem. A transition to a detonation is by no means excluded; actually, it seems to be favored by the physical setting, but a definitive answer would need a full numerical simulation. © 2010 World Scientific Publishing Company.

Richer M.G.,Institute Astronomia
Proceedings of the International Astronomical Union | Year: 2011

The brightest planetary nebulae achieve similar maximum luminosities, have similar ratios of chemcial abundances, and apparently share similar kinematics in all galaxies. These similarities, however, are not necessarily expected theoretically and appear to hide important evolutionary differences. As predicted theoretically, metallicity appears to affect nebular kinematics, if subtly, and there is a clear variation with evolutionary stage. To the extent that it can be investigated, the internal kinematics for galactic and extragalactic planetary nebulae are similar. The extragalactic planetary nebulae for which kinematic data exist, though, probably pertain to a small range of progenitor masses, so there may still be much left to learn, particularly concerning the kinematics of planetary nebulae that descend from the more massive progenitors. © 2012 International Astronomical Union.

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