A COSMOLOGICAL MODEL WITH FERMIONIC FIELD AND GAUSS–BONNET TERM (original) (raw)
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Arxiv preprint arXiv: …, 2009
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Gauss-Bonnet-scalar interaction has been found to play a crucial role from the beginning till the late time of cosmological evolution. A cosmological model has been constructed where the Universe starts with exponential expansion but with infinite deceleration, q → ∞ and infinite equation of state parameter, w → ∞ . During evolution it passes through the stiff fluid era, q = 2, w = 1 , the radiation dominated era, q = 1, w = 1/3 and the matter dominated era, q = 1/2, w = 0 . Finally, deceleration halts, q = 0, w = −1/3 , and it then encounters a transition to the accelerating phase. Asymptotically the Universe reaches yet another inflationary phase q → −1, w → −1 . Such evolution is independent of the form of the potential and the sign of the kinetic energy term ie., even a noncanonical kinetic energy is unable to phantomize (w < −1) the model.
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Cosmological solutions of field equations derived from a ten-dimensional (10D) action containing higher-derivative terms in the Gauss-Bonnet combination have been studied. An attempt has been made to construct a scenario which includes a spontaneous compactification and an inflationary epoch followed by a four-dimensional radiation-dominated stage. It is noted that one can have a realistic scenario, provided there is an inflationary stage of the early 10D universe. A mechanism is suggested which makes the 4D cosmological constant small. The action considered is different from the superstring-corrected action. The study reveals a rich structure of the theory due to the presence of Gauss-Bonnet terms, although one gets back the usual Einstein equation in 4D at a large time.
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Modern Physics Letters A, 2020
Causal cosmological evolutions in Randall Sundrum type II (RS) braneworld gravity with Gauss Bonnet coupling and dissipative effects are discussed here. Causal theory of dissipative effects are illustrated by Full Israel Stewart theory are implemented. We consider the numerical solutions of evolutions and analytic solutions as a special case for extremely non-linear field equation in Randall Sundrum type II braneworld gravity with Gauss Bonnet coupling. Cosmological models admitting Power law expansion, Exponential expansion and evolution in the vicinity of the stationary solution of the universe are investigated for Full Israel Stewart theory. Stability of equilibrium or fixed points related to the dynamics of evolution in Full Israel Stewart theory in Randall Sundrum type II braneworld gravity together with Gauss Bonnet coupling are disclosed here.
Towards inflation and dark energy cosmologies from modified Gauss–Bonnet theory
Journal of Cosmology and Astroparticle Physics - JCAP, 2006
We consider a physically viable cosmological model that has a field dependent Gauss–Bonnet coupling in its effective action, in addition to a standard scalar field potential. The presence of such terms in the four dimensional effective action gives rise to several novel effects, such as a four dimensional flat Friedmann–Robertson–Walker universe undergoing a cosmic inflation at the early epoch, as well as a cosmic acceleration at late times. The model predicts, during inflation, spectra of both density perturbations and gravitational waves that may fall well within the experimental bounds. Furthermore, this model provides a mechanism for reheating of the early universe, which is similar to a model with some friction terms added to the equation of motion of the scalar field, which can imitate energy transfer from the scalar field to matter.
International Journal of Theoretical Physics, 2012
We study a model of scalar field with kinetic terms non-minimally coupled to to the curvature, and the scalar field coupled to the Gauss Bonnet 4-dimensional invariant. A variety of solutions are found, giving rise to different cosmological scenarios. A unified description of early time matter (radiation) dominance with transitions to late time quintessence and phantom phases have been made. Among others, we found solutions unifying asymptotically the early power law behavior and late time cosmological constant. Solutions of Chaplygin gas and generalized Chaplygin gas cosmologies have also been found.
Emergent universe scenario in the Einstein–Gauss–Bonnet gravity with dilaton
General Relativity and Gravitation, 2010
We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss-Bonnet gravity coupled with a dilaton field in four dimensions. The coupling parameter of the Gauss-Bonnet terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the Gauss-Bonnet (GB) terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einsteins static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data.