Thermodynamic analysis of universes with the initial and final de Sitter eras

Abstract

Our aim is studying the thermodynamics of cosmological models including initial and final de-Sitter eras. For this propose, bearing Cai-Kim temperature in mind, we investigate the thermodynamic properties of a dark energy candidate with variable energy density, and show that the state parameter of this dark energy candidate should obey the ωD = −1 constraint, whiles there is no interaction between the fluids filled the universe, and the universe is not in the de-Sitter eras. Additionally, based on thermal fluctuation theory, we study the possibility of inducing fluctuations to the entropy of the dark energy candidate due to a mutual interaction between the cosmos sectors. Therefore, we find a relation between the thermal fluctuations and the mutual interaction between the cosmos sectors, whiles the dark energy candidate has a varying energy density. We point to models in which a gravitationally induced particle production process leads to change the expansion eras, whiles the corresponding pressure is considered as the cause of current acceleration phase. We study its thermodynamics, and show that such processes may also leave thermal fluctuations into the system. We also find an expression between the thermal fluctuations and the particle production rate. Finally, we use Hayward-Kodama temperature to get a relation for the horizon entropy in models including the gravitationally induced particle production process. Our study shows that the first law of thermodynamics is available on the apparent horizon whiles, the gravitationally induced particle production process, as the dark energy candidate, may add an additional term to the Bekenstein limit of the horizon.

Thermodynamical Study of FRW Universe in Quasi-Topological Theory

“…Our study shows that, in quasi-topological gravity theory, a geometrical fluid with energy density ρ e and pressure p e , independent of its nature, affects the apparent horizon entropy as S A = A 4 − 2πnΩ n Hr n+1 A (ρ e + p e )dt, (58) which is in full agreement with other studies [28][29][30][31][32][33][34][35][36]. Since such correction in quasitopological gravity has geometrical nature, it is indeed inevitable.…”

Thermodynamics of universe with a varying dark energy component

“…Moreover, It is shown that the ultimate de-Sitter spacetime is in accordance with the thermodynamic equilibrium conditions, and therefore the cosmos may serve its final stage [38]. In this model, the state parameter of the vacuum energy satisfies the ω D = −1 condition, and thus the vacuum energy decays into the other fields confined to the apparent horizon of the FRW universe [36,39]. It is worthwhile to mention here that the decay of vacuum into the other fields is due to a mutual interaction between the cosmos sectors leading to leave thermal fluctuations into the cosmos in this model [39].…”

“…In continue, Mitra et al extended their hypothesis to other different gravity theories [78]. Moreover, it is also shown that a gravitationally induced particle production process as the DE candidate may change the horizon entropy [39]. Bearing the Lovelock theory in mind, some authors used the T dS A = AΨ − AΨ DE relation to get the entropy of the apparent horizon in cosmological setup [65].…”

“…In this model, the state parameter of the vacuum energy satisfies the ω D = −1 condition, and thus the vacuum energy decays into the other fields confined to the apparent horizon of the FRW universe [36,39]. It is worthwhile to mention here that the decay of vacuum into the other fields is due to a mutual interaction between the cosmos sectors leading to leave thermal fluctuations into the cosmos in this model [39]. It is a good feature, because observations allows a mutual interaction between the cosmos sectors [40][41][42][43][44].…”

“…Thermodynamics of such possible mutual interactions are also studied in various theories of gravity by considering various models for DE [44][45][46][47][48]. In fact, the relation between such possible interactions, coincidence and fine tuning problems and thermal fluctuations attracts more investigators to itself [39,43,48,49].…”