Thermodynamic implications of the gravitationally induced particle creation scenario

Eur. Phys. J. C Thermodynamic implications of the gravitationally induced particle creation scenario Subhajit Saha 1 Anindita Mondal 0 by T H 0 . It has been shown that the GSL is satisfied for H ≤ 1 . Further when is constant thermo- dynamic equilibrium is always possible for H < 1 while for H ≤ min H ≥ 1 equilibrium can never be attained. Thermodynamic arguments also lead us to believe that during the radiation phase ≤ H . When is not a constant thermodynamic equilibrium holds if H¨ ≥ H 1 H 0 however such a condition is by no means necessary for the attainment of equilibrium. 0 Department of Astrophysics and Cosmology, S N Bose National Centre for Basic Sciences , Block-JD, Sector-III, Saltlake, Kolkata 700106, West Bengal , India 1 Department of Physical Sciences, Indian Institute of Science Education and Research Kolkata , Mohanpur 741246, West Bengal , India A rigorous thermodynamic analysis has been done as regards the apparent horizon of a spatially flat Friedmann-Lemaitre-Robertson-Walker universe for the gravitationally induced particle creation scenario with constant specific entropy and an arbitrary particle creation rate . Assuming a perfect fluid equation of state p = (γ − 1)ρ with 23 ≤ γ ≤ 2, the first law, the generalized second law (GSL), and thermodynamic equilibrium have been studied, and an expression for the total entropy (i.e., horizon entropy plus fluid entropy) has been obtained which does not contain explicitly. Moreover, a lower bound for the fluid temperature T f has also been found which is given There have been several attempts to incorporate the present stage of cosmic acceleration into standard cosmology, the most notably being the introduction of an “exotic” component termed dark energy (DE) which is believed to have a huge negative pressure; however, its nature and origin is still a mystery despite extensive research over the past one and a half decades. Several DE models have been proposed in the - literature but observational data from various sources such as supernovae type Ia (SNe Ia), cosmic microwave background (CMB), and baryon acoustic oscillations (BAO) have established that the cosmological constant is the most viable candidate among them. The cosmic concordance CDM model in which the universe is believed to contain a cosmological constant associated with DE, and cold (i.e., pressureless) dark matter (abbreviated CDM) fits rather well the current astronomical data. Nevertheless, there are severe drawbacks corresponding to a finite but incredibly small value of such as the fine-tuning problem which leads to a discrepancy of 50–120 orders of magnitude with respect to its observed value which is about 3 × 10−11 eV4. Then there is the coincidence problem which is related to the question of “why are the energy densities of pressureless matter and DE of the same order precisely at the present epoch although they evolve so differently with expansion?” Several models such as decaying vacuum models, interacting scalar field descriptions of DE, and a single fluid model with an antifriction dynamics have been proposed with a view to alleviate such problems. Moreover, in order to solve the flatness and horizon problems, an inflationary stage for the very early universe was introduced but this again gave rise to several new problems, like the initial conditions, the graceful exit, and multiverse problems. Other attempts to explain the late time accelerating stage are modified gravity models, inhomogeneous cosmological models, etc. but each one of them comes with several problems that are yet to be settled. Because of these said difficulties in various cosmological models, another well known proposal has been suggested—the gravitationally induced particle creation mechanism. Schrödinger [1] pioneered the microscopic description of such a mechanism which was further developed by Parker et al. based on quantum field theory in curved spacetimes [2–6]. Prigogine et al. [7] provided a macroscopic description of particle creation mechanism ) = 0. The non-conservation of the total number N of particles in an open thermodynamic system produces an equation given by n = n . In Eqs. (3) and (4), is the fluid expansion scalar which turns out to be 3H in our case, denotes the rate of change of the number of particles (N = na3) in a comoving volume a3, and n is the number density of particles. So, a positive implies production of particles while a negative indicates particle annihilation. Further, a non-zero produces an effective bulk viscous pressure [21–27] of the fluid and hence non-equilibrium thermodynamics comes into the picture. Using Eqs. (3) and (4), and the Gibbs relation, T ds = d we can obtain an equation relating the creation pressure and the creation rate , which can be expressed as induced by the gravitational field. A covariant description was later proposed [8,9] and the physical difference between particle creation and bulk viscosity was clarified [10]. The proces (...truncated)