Objetos compactos, ultracompactos e exóticos em teorias f(R) da gravitação no formalismo de Palatini

Abstract

We analyze, in the perspective of f(R) Palatini gravity, numeric configurations of spherically symmetric and static stellar objects filled with fluids of isotropic and anisotropic pressure. For such a study, we use the scenario of quadratic f(R) = R+λR2 and two idealization profiles of density as a first step in this direction. Initially, we investigate in the isotropic case, the behavior of isotropic pressure and geometry inside of such ob jects from a density profile that which is almost constant inside the object, but decays on the surface of it. We also discussed the trapped null geodesics in scope of compact and ultracompact objects. We explore separately, configurations of star filled with fluid of anisotropic pressure, where we analyze behaviors of geometry, radial and tangential pressure inside of the object. For this purpose, we use a parameter of anisotropy in particular and a profile of density different from isotropic case. The fact we can reach values of negative pressure when we are working with anisotropic pressure also allows us to study configurations of exotic objects as “gravastars”. The obtained results in both cases were compared with general relativity, enabling us to analyze the existence, in the space of parameters, of configurations of objects more, less or as compact as results of general relativity for the same density. In isotropic case, we also analyze the possibility of obtaining configurations beyond Buchdahl’s limit of general relativity.