Akademik Veri Yönetim Sistemi
Gravitation and Cosmology, cilt.25, sa.4, ss.397-406, 2019 (SCI-Expanded)
Using variable gravitational and cosmological constants, the mechanism of particle creation in the universe is studied for Friedmann–Robertson–Walker (FRW) space-times at high dimensions to explain the early deceleration and present accelerating phases. To investigate the dynamics of these phases, we consider two scale factor of the forms a(t)=tαet and a(t)=sinh(kt)m, which yield two different time-dependent deceleration parameters. Firstly, we modify the d-dimensional time-dependent field equations, including the general formulation of particle creation and entropy generation mechanisms. Then, we investigate the time dependence of a few quantities such as the particle creation rate ψ, the entropy S, the gravitational constant G, the cosmological constant Λ, the energy density ρ, the deceleration parameter q, etc. We show that all constants and quantities, except the gravitational constant G and the entropy S, characteristically decrease with time for two kinds of scale factors in all dimensions. However, the gravitational constant G and the entropy S increase with time. Additionally, we show that the cosmological constant Λ is unexpectedly independent of the particle creation mechanism, unlike G.