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Full-Text Articles in Physics
Reheating Constraints To Palatini Coleman-Weinberg Inflation, Nilay Bostan
Reheating Constraints To Palatini Coleman-Weinberg Inflation, Nilay Bostan
Turkish Journal of Physics
In this work, we examine the reheating constraints to symmetry-breaking mechanism, which is associated with Coleman-Weinberg inflation in the early universe. We consider the Coleman-Weinberg inflation potential, where the inflaton has a v ̸= 0 after inflation. Setting Treh = 105 GeV, we first show wreh dependency on ns , r , and N∗ for AV case. Then, we demonstrate the results of ns , r , N∗ , α = dns/d ln k for different reheating temperatures and compare the results with the latest BICEP/Keck data. We also present that ns −r and ns −N∗ planes and the effect …
Thermodynamics Of Cosmological Models With Generalized $G$ And $\Lambda $, M Saratchandra Singh, Sanasam Surendra Singh
Thermodynamics Of Cosmological Models With Generalized $G$ And $\Lambda $, M Saratchandra Singh, Sanasam Surendra Singh
Turkish Journal of Physics
Here we investigate spatially flat Friedmann-Robertson-Walker space-time models of the universe to study the thermodynamic behaviors in light of variables $G$ and $\Lambda $. A particular method to find the solutions of Einstein's field equations and mathematical expressions for temperature and entropy of the perfect fluid cosmological models is introduced by using both the equation of state and the assumption $G=G_{0} \,a^{n}$. It is observed that the phantom field of ($\omega
Nature Of Entropy In A Scalar-Tensor Theory Of Gravity, Onur Siğinç, Mustafa Salti, Hi̇lmi̇ Yanar, Oktay Aydoğdu
Nature Of Entropy In A Scalar-Tensor Theory Of Gravity, Onur Siğinç, Mustafa Salti, Hi̇lmi̇ Yanar, Oktay Aydoğdu
Turkish Journal of Physics
This work is devoted to studying the generalized nature of the entropy function in a specific form of the scalar-tensor-vector (STeVe) theory of gravity for the Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime in the state of thermal equilibrium. For this purpose, we define an equilibrium picture of thermodynamics by making use of a suitable set of the dark energy density and dark pressure descriptions, which defines an energy-momentum tensor obeying the local energy conservation law. Furthermore, we also discuss our results numerically in order to get additional implications.
It Is Sufficient To Set The Cosmological Constant To Zero Or To A Small Number At An Initial Time, Recai̇ Erdem
It Is Sufficient To Set The Cosmological Constant To Zero Or To A Small Number At An Initial Time, Recai̇ Erdem
Turkish Journal of Physics
I point out a simple but usually overlooked fact about the cosmological constant problem: to solve the cosmological constant problem it is sufficient to find a symmetry or mechanism that sets the cosmological constant to zero or to a tiny value at some time in the past, provided that general relativity is the relevant theory of gravity, and the energy-momentum tensor (excluding the part of the form of a cosmological constant) is conserved. The relevant symmetry or mechanism need not be applicable today. Any additional cosmological constant term induced by a phase transition in the energy-momentum tensor in this case …
Bianchi-V Cosmological Models With Viscous Fluid And Constant Deceleration Parameter In General Relativity, Sharad Kandalkar, Pramod Khade, Mohini Gaikwad
Bianchi-V Cosmological Models With Viscous Fluid And Constant Deceleration Parameter In General Relativity, Sharad Kandalkar, Pramod Khade, Mohini Gaikwad
Turkish Journal of Physics
In this paper we discuss the variation law for Hubble's parameter, average scale factor in spatially homogenous anisotropic Bianchi Type V space-time that yields a constant value deceleration parameter. Using the law of variation for Hubble's parameter, exact solutions of Einstein's field equations are obtained for Bianchi-V space time filled with viscous fluid in two different cases where the universe exhibits power law and exponential expansion. We investigate a number of solutions with constant and time varying cosmological constant together with variable and constant bulk viscosity. We find that the constant value of deceleration parameter is reasonable for the present …
On Robertson-Walker Universe Model With Variable Cosmological Term And Gravitational Constant In Cosmological Relativity Theory, Kangujam Priyokumar Singh
On Robertson-Walker Universe Model With Variable Cosmological Term And Gravitational Constant In Cosmological Relativity Theory, Kangujam Priyokumar Singh
Turkish Journal of Physics
This paper presents cosmological models in which the gravitational and cosmological constants G and \Lambda are time-dependent. We find a variety of solutions for the variation of cosmological parameters. It is also found that, in the case of matter dominated Robertson-Walker Universe, if the cosmological constant \Lambda \ne 0, the Hubble's constant H is not constant at all but inversely proportional to the cosmic time. The conservation law for the energy momentum tensor is still valid with our law of variation: \Lambda \propto R^{-2} and G\rho \propto \frac{\Lambda }{8\pi}.
Kantowski-Sachs Viscous Fluid Cosmological Model With A Varying \Lambda, Sharad Kandalkar, Pramod Khade, Sunita Gawande
Kantowski-Sachs Viscous Fluid Cosmological Model With A Varying \Lambda, Sharad Kandalkar, Pramod Khade, Sunita Gawande
Turkish Journal of Physics
We study the Kantowski-Sachs cosmological model filled with viscous fluid in the presence of cosmological term \Lambda. To get a deterministic solution, a condition between metric potentials is used. The viscous coefficient of bulk viscous fluid is assumed to be a power function of mass density, whereas coefficient of shear viscosity is considered proportional to scale of expansion in the model. It is found that the cosmological constant \Lambda is positive and is a decreasing function of time, which is supported by results from recent supernova observations. Some physical and geometrical properties of the models are also discussed.