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Register a new userCoupled Quintessence and Phantom Based On a Dilaton
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Based on dilatonic dark energy model, we consider two cases: dilaton field with positive kinetic energy(coupled quintessence) and with negative kinetic energy(phantom). In the two cases, we investigate the existence of attractor solutions which correspond to an equation of state parameter $omega=-1$ and a cosmic density parameter $Omega_sigma=1$. We find that the coupled term between matter and dilaton cant affect the existence of attractor solutions. In the Mexican hat potential, the attractor behaviors, the evolution of state parameter $omega$ and cosmic density parameter $Omega$, are shown mathematically. Finally, we show the effect of coupling term on the evolution of $X(frac{sigma}{sigma_0})$ and $Y(frac{dot{sigma}}{sigma^2_0})$ with respect to $N(lna)$ numerically.
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In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as coupled Quintessence, which is called DCQ model by us. Parametrization of the dark energy model is a good method by which we can construct the scalar potential directly from the effective equation of state function $omega_sigma(z)$ describing the properties of the dark energy. Applying this method to the DCQ model, we consider four parametrizations of $omega(z)$ and investigate the features of the constructed DCQ potentials, which possess two different evolutive behaviors called O mode and E mode. Lastly, we comprise the results of the constructed DCQ model with those of quintessence model numerically.
In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as a coupled quintessence. Based on this consideration, we investigate the dilaton coupled quintessence(DCQ) model in $omega-omega$ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to $N$(the logarithm of the scale factor $a$). We find the scalar field equation of motion in $omega-omega$ plane, and show mathematically the property of attractor solutions which correspond to $omega_sigmasim-1$, $Omega_sigma=1$. Finally, we find that our model is a tracking one which belongs to freezing type model classified in $omega-omega$ plane.
We investigate charged black holes coupled to a massive dilaton. It is shown that black holes which are large compared to the Compton wavelength of the dilaton resemble the Reissner-Nordstrom solution, while those which are smaller than this scale resemble the massless dilaton solutions. Black holes of order the Compton wavelength of the dilaton can have wormholes outside the event horizon in the string metric. Unlike all previous black hole solutions, nearly extremal and extremal black holes (of any size) repel each other. We argue that extremal black holes are quantum mechanically unstable to decay into several widely separated black holes. We present analytic arguments and extensive numerical results to support these conclusions.
We consider the propagation of electromagnetic waves through a dilaton-Maxwell domain wall of the type introduced by Gibbons and Wells [G.W. Gibbons and C.G. Wells, Class. Quant. Grav. 11, 2499-2506 (1994)]. It is found that if such a wall exists within our observable universe, it would be absurdly thick, or else have a magnetic field in its core which is much stronger than observed intergalactic fields. We conclude that it is highly improbable that any such wall is physically realized.
We explore a cyclic universe due to phantom and quintessence fields. We find that, in every cycle of the evolution of the universe, the phantom dominates the cosmic early history and quintessence dominates the cosmic far future. In this model of universe, there are infinite cycles of expansion and contraction. Different from the inflationary universe, the corresponding cosmic space-time is geodesically complete and quantum stable. But similar to the Cyclic Model, the flatness problem, the horizon problem and the large scale structure of the universe can be explained in this cyclic universe.
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