Curvas de rotação galácticas em teorias métricas da gravitação

Abstract

From a Parametrized Post-Newtonian (PNP) perspective we attempt to partially answer the question, by studying some models, of whether or not the new degrees of freedom, represented by the PNP potentials, can lead to significant modifications in the dynamics of galaxies in the direction of rendering dark matter obsolete. In the PNP, several parameters classify each theory and their possible values are tightly constrained mainly due to solar system experiments [ 1 , 2 , 3 ]. Such restrictions renders the modifications of gravitational effects, with respect to General Relativity, to be insignificant, making attempts to find alternative metrical theories rather fruitless. In recent years a new kind of metric theories have arisen to popularity and are characterized by "Screening" mechanisms [ 4 ]. These lead to the possibility of modifications in larger scales than the solar system while retaining the success of GR in the latter, allowing for violations of the constraints of the Post-Newtonian parameters. With this new paradigm we consider two kinds of solutions: (i) When no matter field is present, or in other words, vacuum; (ii) or a Politropic distribution of matter. For (i) we find that the corrections don’t lead to the needed modifications as required to be an alternative to dark matter. In (ii) for most choices of the parameters (when changing γ , β , ξ , α 3 , ζ j , with j = 1 , 2, from their values in GR) the need for dark matter is unavoidable, in order to find a flat rotation curve. It’s only for theories in which ζ 3 > 0 that some resemblance of flat rotation curves is found. The latter suggests, at least for the models considered, that these are the only theories capable of replacing dark matter as a possible explanation for the dynamics of galaxies.