3 research outputs found
Exact spherically symmetric solutions in modified Gauss-Bonnet gravity from Noether symmetry approach
It is broadly known that Lie point symmetries and their subcase, Noether
symmetries, can be used as a geometric criterion to select alternative theories
of gravity. Here, we use Noether symmetries as a selection criterion to
distinguish those models of theory, with and being the Ricci
and the Gauss-Bonnet scalars respectively, that are invariant under point
transformations in a spherically symmetric background. In total, we find ten
different forms of that present symmetries and calculate their invariant
quantities, i.e Noether vector fields. Furthermore, we use these Noether
symmetries to find exact spherically symmetric solutions in some of the models
of theory.Comment: 17 pages. Accepted for Publication in Symmetries in the special issue
"Noether's symmetry approach in gravity and cosmology
Cosmological perturbations in f(G) gravity
We explore cosmological perturbations in a modified Gauss-Bonnet f(G)
gravity, using a 1+3 covariant formalism. In such a formalism, we define
gradient variables to get perturbed linear evolution equations. We transform
these linear evolution equations into ordinary differential equations using a
spherical harmonic decomposition method. The obtained ordinary differential
equations are time-dependent and then transformed into redshift dependent.
After these transformations, we analyze energy-density perturbations for
two-fluid systems, namely for a Gauss-Bonnet field-dust system and for a
Gaus-Bonnet field-radiation system for three different pedagogical f(G) models:
trigonometric, exponential, and logarithmic. For the Gauss-Bonnet field-dust
system, energy-density perturbations decay with an increase in redshift for all
three models. For the Gauss-Bonnet field-radiation system, the energy-density
perturbations decay with an increase in redshift for all of the three f(G)
models for long-wavelength modes whereas for short-wavelength modes, the
energy-density perturbations decay with increasing redshift for the logarithmic
and exponential f(G) models and oscillate with decreasing amplitude for the
trigonometric f(G) model.Comment: 32 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1801.01758 by other author