15,162 research outputs found

    A method for evaluating models that use galaxy rotation curves to derive the density profiles

    Full text link
    There are some approaches, either based on General Relativity (GR) or modified gravity, that use galaxy rotation curves to derive the matter density of the corresponding galaxy, and this procedure would either indicate a partial or a complete elimination of dark matter in galaxies. Here we review these approaches, clarify the difficulties on this inverted procedure, present a method for evaluating them, and use it to test two specific approaches that are based on GR: the Cooperstock-Tieu (CT) and the Balasin-Grumiller (BG) approaches. Using this new method, we find that neither of the tested approaches can satisfactorily fit the observational data without dark matter. The CT approach results can be significantly improved if some dark matter is considered, while for the BG approach no usual dark matter halo can improve its results.Comment: 11 pages, 2 figures, 4 tables. v2: diverse text improvements, no changes in the conclusions. Version accepted in MNRA

    Efeito da adubação nitrogenada, arranjo de plantas e redutor de crescimento no acamamento e em características de cevada.

    Get PDF
    bitstream/CNPT-2010/40293/1/p-bp20.pd

    On the κ\kappa-Dirac Oscillator revisited

    Get PDF
    This Letter is based on the κ\kappa-Dirac equation, derived from the κ\kappa-Poincar\'{e}-Hopf algebra. It is shown that the κ\kappa-Dirac equation preserves parity while breaks charge conjugation and time reversal symmetries. Introducing the Dirac oscillator prescription, ppimωβr\mathbf{p}\to\mathbf{p}-im\omega\beta\mathbf{r}, in the κ\kappa-Dirac equation, one obtains the κ\kappa-Dirac oscillator. Using a decomposition in terms of spin angular functions, one achieves the deformed radial equations, with the associated deformed energy eigenvalues and eigenfunctions. The deformation parameter breaks the infinite degeneracy of the Dirac oscillator. In the case where ε=0\varepsilon=0, one recovers the energy eigenvalues and eigenfunctions of the Dirac oscillator.Comment: 5 pages, no figures, accepted for publication in Physics Letters
    corecore