1,720,974 research outputs found
Noether symmetry approach in pure gravity with variable G and Lambda
No full textWe find exact cosmological solutions when the Newton parameter and the
cosmological term dynamically evolve in a renormalization-group improved
Hamiltonian approach. In our derivation we use the Noether symmetry
approach, leading to an interesting variable transformation which yields
exact and general integration of the cosmological equations. The functional
dependence of Lambda on G is determined by the method itself, therefore generalizing
previous results on symmetry principles in cosmology. We find new functional
relations between Lambda and G, jointly with power-law inflation for pure gravity
Dark energy exponential potential models as curvature quintessence
No full textIt has been recently shown that, under some general conditions, it is always possible to find a fourth-order gravity theory capable of reproducing the same dynamics as a given dark energy model. Here, we discuss this approach for a dark energy model with a scalar field evolving under the action of an exponential
potential. In the absence of matter, such a potential can be recovered from a fourth-order theory via a conformal transformation. Including the matter term, the function f (R) entering the generalized gravity Lagrangian can be
reconstructed according to the dark energy model
Gauge invariant perturbations of scalar-tensor cosmologies: The vacuum case
No full textThe covariant gauge-invariant perturbation theory of scalar cosmological perturbations is developed for a general scalar-tensor Friedmann-Lemaitre- Robertson-Walker cosmology in a vacuum. The perturbation equations are then solved exactly in the long wavelength limit for a specific coupling, potential, and background. Differences with the minimally coupled case are briefly discussed. © 2006 The American Physical Society
Accelerating universe in scalar tensor models - comparison of theoretical predictions with observations
No full textNoether symmetry approach in matter-dominated cosmology with variable G and Lambda
No full textIn the framework of renormalization-group improved cosmologies,
we use the Noether symmetry approach to get exact and general integration
of the matter-dominated cosmological equations. This is performed by using
an expression of Lambda = Lambda(G) determined by the method itself. We also work
out a comparison between such a model and the concordance LambdaCDM model
as to the magnitude–redshift relationship, hence showing that no appreciable
differences occur
Noether symmetry in the higher order gravity theory
No full textWe explore the conditions for the existence of Noether symmetries for higher order gravity theory, after introducing an auxiliary variable, which gives the correct quantum description of the theory. It turns out that the application of Noether theorem in higher order theory of gravity is a powerful tool to find the solution of the field equations. A few such physically reasonable solutions like
power law inflation are presented
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