22,435 research outputs found

    An alternative approach concerning Elko spinors and the hidden unitarity

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    In this theoretical communication we look towards understand the underlying phenomenology concerning the Elko spinors within VSR theory. The program to be accomplished here start when we define the eigenspinors of the charge conjugation operator as eigenstates of the helicity operator in the Cartesian coordinates system. This prescription is very useful in the sense of phenomenological point of view, so, we propose a set of Elko spinors ready to be computationally implemented. Regardless of, in order to show the application of given approach we impose to these spinors to be restrict to an axis, coincidentally the axis of locality, and then, using the proposed prescription, we search for physical amounts and physical processes by analysing the Yukawa and the self-interaction in such framework.Comment: 10 pages, 2 figures. Accepted for publication in AAC

    Born-Infeld magnetars: larger than classical toroidal magnetic fields and implications for gravitational-wave astronomy

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    Magnetars are neutron stars presenting bursts and outbursts of X- and soft-gamma rays that can be understood with the presence of very large magnetic fields. Thus, nonlinear electrodynamics should be taken into account for a more accurate description of such compact systems. We study that in the context of ideal magnetohydrodynamics and make a realization of our analysis to the case of the well-known Born-Infeld (BI) electromagnetism in order to come up with some of its astrophysical consequences. We focus here on toroidal magnetic fields as motivated by already known magnetars with low dipolar magnetic fields and their expected relevance in highly magnetized stars. We show that BI electrodynamics leads to larger toroidal magnetic fields when compared to Maxwell's electrodynamics. Hence, one should expect higher production of gravitational waves (GWs) and even more energetic giant flares from nonlinear stars. Given current constraints on BI's scale field, giant flare energetics and magnetic fields in magnetars, we also find that the maximum magnitude of magnetar ellipticities should be 10−6−10−510^{-6}-10^{-5}. Besides, BI electrodynamics may lead to a maximum increase of order 10%−20%10\%-20\% of the GW energy radiated from a magnetar when compared to Maxwell's, while much larger percentages may arise for other physically motivated scenarios. Thus, nonlinear theories of the electromagnetism might also be probed in the near future with the improvement of GW detectors.Comment: 8 pages, no figures, accepted for publication in The European Physical Journal C (EPJC

    On the nature of some SGRs and AXPs as rotation-powered neutron stars

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    We investigate the possibility that some SGRs/AXPs could be canonical rotation-powered pulsars using realistic NS structure parameters instead of fiducial values. We show that realistic NS parameters lowers the estimated value of the magnetic field and radiation efficiency, LX/E˙rotL_X/\dot{E}_{\rm rot}, with respect to estimates based on fiducial NS parameters. We show that nine SGRs/AXPs can be described as canonical pulsars driven by the NS rotational energy, for LXL_X computed in the soft (2--10~keV) X-ray band. We compute the range of NS masses for which LX/E˙rot<1L_X/\dot{E}_{\rm rot}<1. We discuss the observed hard X-ray emission in three sources of the group of nine potentially rotation-powered NSs. This additional hard X-ray component dominates over the soft one leading to LX/E˙rot>1L_X/\dot{E}_{\rm rot}>1 in two of them. We show that 9 SGRs/AXPs can be rotation-powered NSs if we analyze their X-ray luminosity in the soft 2--10~keV band. Interestingly, four of them show radio emission and six have been associated with supernova remnants (including Swift J1834.9-0846 the first SGR observed with a surrounding wind nebula). These observations give additional support to our results of a natural explanation of these sources in terms of ordinary pulsars. Including the hard X-ray emission observed in three sources of the group of potential rotation-powered NSs, this number of sources with LX/E˙rot<1L_X/\dot{E}_{\rm rot}<1 becomes seven. It remains open to verification 1) the accuracy of the estimated distances and 2) the possible contribution of the associated supernova remnants to the hard X-ray emission.Comment: 11 pages, 14 figures, to appear in A&

    Influência dos fatores edáficos no crescimento da Bertholletia excelsa H.B.K. na Amazônia.

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    O objetivo deste trabalho foi determinar a influência dos fatores edáficos (físicos e químicos) na variabilidade do crescimento da Bertholletia excelsa H.B.K. (castanheira-do-brasil) em distintas condições de solo na Amazônia

    Teste de germinação in vitro de embriões zigóticos de dendezeiro.

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    Este trabalho teve como objetivo avaliar a germinação e a viabilidade de sementes de E. guineensis, por meio de ensaios in vitro e teste de tetrazólio de embriões zigóticos
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