25 research outputs found
Considering Late-Time Acceleration in some Cosmological Models
We study two cosmological models: A non-minimally coupled scalar field on
brane world model and a minimally coupled scalar field on Lorentz invariance
violation model. We compare some cosmological results in these scenarios. Also,
we consider some types of Rip singularity solution in both models.Comment: 14 pages, 10 figures, Accepted for Publication in Adv. High Energy
Phy
Dark Energy Density and IS (Israel-Stewart) Bulk Viscosity Model
We investigate the thermodynamics of a dark energy bulk viscosity model as a
cosmic fluid. In this regard, the two theories of Eckart and Israel-Stewart
(IS) are the basis of our work. Therefore, we first investigate the
thermodynamics of cosmic fluids in the dark energy bulk viscosity model and the
general relationships. Then, we express the thermodynamic relationships of
Eckart's theory. Due to the basic equations of Eckart's theory and Friedmann's
equations, we consider two states, one is (standard) and the other is
(non-standard). In the standard state, we define the pressure
, energy density , and bulk viscosity coefficient of the
cosmic fluid in terms of cosmic time and we obtain its relations. We also
mention that in this standard state, because of , the value of
is zero, so is not defined in this state. But in the non-standard case
the bulk viscosity coefficient is zero and only the
scale factor and pressure and energy density of the cosmic fluid is defined. We
also consider two states of constant and variable bulk viscosity coefficients
and obtain three Hubble constant parameters and scale factors in terms of
cosmic time, and energy density in terms of the scale factor. In the state of
variable bulk viscosity coefficient, we consider the viscosity coefficient as
the power-law from energy density , which is
and a constant. Following, we discuss the dissipative effects of cosmic fluids
and examine the effects of energy density for dark energy in the
Israel-Stewart(IS) theory. The results are comprehensively presented in two
tables (1) and (2).Comment: 28 pages, 11 figurs, 2 table
Bouncing universe with a non-minimally coupled scalar field on a moving domain wall
AbstractWe study dynamics of a dark energy component non-minimally coupled to gravity on a moving domain wall. We use this setup to explain late-time accelerated expansion and crossing of the phantom divide line by the equation of state parameter of this non-minimally coupled dark energy component. By analyzing parameter space of the model, we show that this model accounts for accelerated expansion and crossing of the phantom divide line with a suitable fine-tuning of the non-minimal coupling. Then we study the issue of bouncing solutions in this framework
Agegraphic Model based on the Generalized Uncertainty Principle
Many models of dark energy have been proposed to describe the universe since
the beginning of the Big Bang. In this study, we present a new model of
agegraphic dark energy () based on the three generalized uncertainty
principles (Kempf, Mangan, Mann), Nouicer and ( higher orders
generalized uncertainty principle).Using the obtained relations from three of
types of , in the form of three
scenarios(Emergent,Intermediate,Logamediate), we consider three different eras
of the universe evolution. Also we describe the evolution and expansion of the
universe in each subsection. We will plot the obtained relations in these
models for better comparatione.Comment: 23 pages, 28 figures, Accepted for publication in IJGMM
Non-Minimal Inflation after WMAP3
The Wilkinson Microwave Anisotropy Probe (WMAP) three year results are used
to constraint non-minimal inflation models. Two different non-minimally coupled
scalar field potentials are considered to calculate corresponding slow-roll
parameters of non-minimal inflation. The results of numerical analysis of
parameter space are compared with WMAP3 data to find appropriate new
constraints on the values of the non-minimal coupling. A detailed comparison of
our results with previous studies reveals the present status of the non-minimal
inflation model after WMAP3.Comment: 16 pages, 11 figures, 2 tables, Revised Versio
A Lorentz Invariance Violating Cosmology on the DGP Brane
We study cosmological implications of a Lorentz invariance violating
DGP-inspired braneworld scenario. A minimally coupled scalar field and a
single, fixed-norm, Lorentz-violating timelike vector field within an
interactive picture provide a wide parameter space which accounts for late-time
acceleration and transition to phantom phase of the scalar field.Comment: 23 pages, 8 figures, accepted for publication in JCA
Loop Quantum Gravity Modification of the Compton Effect
Modified dispersion relations(MDRs) as a manifestation of Lorentz invariance
violation, have been appeared in alternative approaches to quantum gravity
problem. Loop quantum gravity is one of these approaches which evidently
requires modification of dispersion relations. These MDRs will affect the usual
formulation of the Compton effect. The purpose of this paper is to incorporate
the effects of loop quantum gravity MDRs on the formulation of Compton
scattering. Using limitations imposed on MDRs parameters from Ultra High Energy
Cosmic Rays(UHECR), we estimate the quantum gravity-induced wavelength shift of
scattered photons in a typical Compton process. Possible experimental detection
of this wavelength shift will provide strong support for underlying quantum
gravity proposal.Comment: 12 pages, 2 eps figures, revised versio