5 research outputs found
Cosmological Evolution in 1/R-Gravity Theory
Recently, corrections of the type to Einstein-Hilbert action that
become important at small curvature are proposed. Those type of models intend
to explain the observed cosmic acceleration without dark energy. We derive the
full Modified Friedmann equation in the Palatini formulation of those modified
gravity model of the type. Then, we discuss various cosmological
predictions of the Modified Friedmann equation.Comment: 7 pages, 5 figures. Accepted for publication in Class.Quant.Gra
Modified Friedmann Equations in R-Modified Gravity
Recently, corrections to Einstein-Hilbert action that become important at
small curvature are proposed. We discuss the first order and second order
approximations to the field equations derived by the Palatini variational
principle. We work out the first and second order Modified Friedmann equations
and present the upper redshift bounds when these approximations are valid. We
show that the second order effects can be neglected on the cosmological
predictions involving only the Hubble parameter itself, e.g. the various
cosmological distances, but the second order effects can not be neglected in
the predictions involving the derivatives of the Hubble parameter. Furthermore,
the Modified Friedmann equations fit the SN Ia data at an acceptable level.Comment: 15 pages, 6 figures, v2: discussion added; v3: minor changes,
accepted by Class. and Quan. Gra
Dark Energy Model with Spinor Matter and Its Quintom Scenario
A class of dynamical dark energy models, dubbed Spinor Quintom, can be
constructed by a spinor field with a nontraditional potential. We find
that, if choosing suitable potential, this model is able to allow the
equation-of-state to cross the cosmological constant boundary without
introducing any ghost fields. In a further investigation, we show that this
model is able to mimic a perfect fluid of Chaplygin gas with during
the evolution, and also realizes the Quintom scenario with its
equation-of-state across -1.Comment: 20 pages, 5 figures, accepted by CQG, several references adde