FRW Bulk Viscous Cosmology in Non-flat Universe

In this paper we consider FRW bulk viscous cosmology in arbitrary space curvature. We extend recent work to the case of non-flat universe in arbitrary space dimension. We obtain Hubble expansion parameter for special cases and study bulk viscous coefficient and deceleration parameter.     

Thermodynamics of New Modified Chaplygin Gas in Magnetic FRW Universe

We study the generalized second law of thermodynamics in the presence of non-interacting magnetic field and new modified Chaplygin gas with FRW universe. In this scenario, we investigate the validity of this law on Hubble, apparent, particle and event horizons. It is found that this law is respected on all horizons for specific values of the model parameters except on the event horizon where it does not hold for short time but remains valid otherwise. Finally, we explore the statefinders and Om diagnostic to check the viability of the present cosmological model.     

Mechanical and Thermal Properties of the AH of FRW Universe

We calculate the work made out by the apparent horizon （AH） of the Friedmann-Robertson-Walker （FRW） universe and the heat flux through the AH from the first law of thermodynamics. We discuss the mechanical properties of the AH and analyze the universe model for which the mechanical properties can change. Finally, the thermal properties of the AH of FRW universe are discussed.     

Thermodynamics of the Apparent Horizon in FRW Universe with Massive Gravity

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive gravity model in cosmology proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified Misner-Sharp internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation δQ=TdS, where the heat flow δQ is the energy-supply of pure matter projecting on the vector ξ tangent to the apparent horizon and should be looked on as the amount of energy crossing the apparent horizon during the time interval dt and the temperature of the apparent horizon for energy crossing during the same interval is 1/(2πA), the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit Hc→0, which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if α3+4α40. Without this condition, even for the simplest model of dRGT massive cosmology with α3 =α4 =0, the generalized second law of thermodynamics could be violated.     

Thermodynamics of the Apparent Horizon in FRW Universe with Massive Gravity

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive gravity model in cosmology proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified Misner-Sharp internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation δQ=T dS, where the heat flow δQ is the energy-supply of pure matter projecting on the vector ζ tangent to the apparent horizon and should be looked on as the amount of energy crossing the apparent horizon during the time interval dt and the temperature of the apparent horizon for energy crossing during the same interval is 1/2πrA, the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit H_c→0, which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if α₃+4α₄<0. Without this condition, even for the simplest model of dRGT massive cosmology with α₃=α₄=0, the generalized second law of thermodynamics could be violated.     

Exact Solutions for the Fluctuations in a Flat FRW Universe Coupled to a Scalar Field

Some exact solutions for the small-first-order perturbations of an FRW metric minimally coupled to a neutral massive scalar field are presented.     

Letter: Quantum Mechanics Forbids Singularities in a Closed Radiation-dominated FRW Universe

The existence of singularities in a closed FRWuniverse depends on the assumption that generalrelativity is valid for distances less than the Plancklength. However, the stationary state wave functions of the Schrodinger equation for a closedradiation-dominated FRW universe derived by Elbaz et al.are zero at zero radius of curvature. Thus, even ifgeneral relativity is assumed valid at distances less than the Planck length, quantum mechanics seems to forbid singularities in a closed radiation-dominatedFRW universe.     

Hawking Radiation of Apparent Horizon in a FRW Universe as Tunneling Beyond Semiclassical Approximation

An analysis of Hawking radiation about apparent horizon in a FRW universe is performed by using the method developed in the paper (Banerjee, Majhi in JHEP 06:095 2008), in which the Hawking radiation of a black hole is treated as the quantum tunneling by Hamilton-Jacobi method beyond semiclassical approximation and then all the higher order quantum corrections can be given out. In our analysis, the Kodama vector instead of the Killing vector to define the energy of the particle plays a key role. We present our analysis under the Friedmann-Robertson-Walker like coordinate system and the much-like to Painlevé coordinate system respectively. The result show that the formulized procedure can be extended to fully analyse the Hawking radiation of a dynamical system.     

Spin Zero Quantum Relativistic Particles in Einstein Universe

We find exact eigenvalues and eigenfunctions of relativistic massless scalar particle conformally coupled to a background Einstein universe.     

An Interacting and Non-interacting Two-Fluid Dark Energy Models in FRW Universe with Time Dependent Deceleration Parameter

We study the evolution of the dark energy parameter in a spatially homogeneous and isotropic FRW space-time filled with barotropic fluid and dark energy by considering a time dependent deceleration parameter. Two cases are discussed when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. It is concluded that in both non-interacting and interacting cases only open and flat universes cross the phantom region. We find that during the evolution of the universe, the equation of state (EoS) for dark energy ω _D changes from ω _D >−1 to ω _D <−1, which is consistent with recent observations. The cosmic jerk parameter in our derived models is also found to be in good agreement with the recent data of astrophysical observations.     

Quantum Creation of Highly Massive Particles in the Very Early Universe

Quantum creation of very massive particles in the gravitational background of anisotropically perturbed Minkowski space-time is discussed. In this framework of semiclassical gravity the quantum mechanically produced heavy particles which made the initial space-time unstable and ushered into the FRW expansion phase at the Planck order epoch of the universe can account for the energy density at that epoch. Also, both the conformal and nonconformal particle-creations in the FRW era of the early universe after the Planck order epoch are investigated. In this consideration the total particle number of the observable universe as well as the present value of photon-to-baryon ratio are obtained in agreement with their accepted values from the observational facts. The existence of very massive particles at the very early period of the universe is also discussed here with the suggestion of an observational test.     

Production of the Matter in the Early Universe

A gravitational analog of the nonstationary perturbation theory is developed within which the production of the scalar-field massive quanta by gravitational atoms is studied.     

The Production of Pseudo Goldstone Boson in Top Quark Rare Decay

We calculate the flavor changing t → cπ0 decay in the framework of the topcolor assisted multiscaletechnicolor model. We find that (a) the branching ratio of t → cπ0 is insensitive to mπ, mπs and mπt, while it increasesquickly as ε increases; (b) for reasonable ranges of the parameters, the maximum of the branching ratio in this modelmay reach 7 × 10-6, seven orders larger compared to the one t → cH0 calculated in the standard model. This mightprovide an opportunity to detect the rare decay of the top quark in experiments.     

The Generalized Second Law for the Interacting New Agegraphic Dark Energy in a Non-flat FRW Universe Enclosed by the Dynamical Apparent Horizon

We investigate the validity of the generalized second law of gravitational thermodynamics on the dynamical apparent horizon in a non-flat FRW universe containing the interacting new agegraphic dark energy with dark matter. We show that for this model, the equation of state parameter can cross the phantom divide line. We also present that for the selected model under thermal equilibrium with the Hawking radiation, the generalized second law is always satisfied throughout the history of the universe. Whereas, the evolution of the entropy of the universe and dynamical apparent horizon, separately, depends on the equation of state parameter of the interacting new agegraphic dark energy model.     

A Note on Friedmann Equation of FRW Universe in DeformedHo\v{r}ava-Lifshitz Gravity from Entropic Force

With entropic interpretation of gravity proposed by Verlinde, we obtain the Friedmann equation of the Friedmann-Robertson-Walker universe for the deformed Ho\v{r}ava-Lifshitz gravity. It is shown that, when the parameter of Ho\v{r}ava-Lifshitz gravityω→∝, the modified Friedmann equation will go back to the one in Einstein gravity. This results may imply that the entropic interpretation of gravity is effective for the deformed Ho\v{r}ava-Lifshitz gravity.