Abstract
We consider the possibility of a gravitationally induced particle production through the mechanism of a nonminimal curvature-matter coupling. An interesting feature of this gravitational theory is that the divergence of the energy-momentum tensor is nonzero. As a first step in our study we reformulate the model in terms of an equivalent scalar-tensor theory, with two arbitrary potentials. By using the formalism of open thermodynamic systems, we interpret the energy balance equations in this gravitational theory from a thermodynamic point of view, as describing irreversible matter creation processes. The particle number creation rates, the creation pressure, and the entropy production rates are explicitly obtained as functions of the scalar field and its potentials, as well as of the matter Lagrangian. The temperature evolution laws of the newly created particles are also obtained. The cosmological implications of the model are briefly investigated, and it is shown that the late-time cosmic acceleration may be due to particle creation processes. Furthermore, it is also shown that due to the curvature--matter coupling, during the cosmological evolution a large amount of comoving entropy is also produced.
Highlights
In [4], the correspondence between cosmological models powered by a decaying vacuum energy density and gravitationally induced particle production was explored
By multiplying Eq (23) with U ν we obtain the energy balance equation in the scalar–tensor representation of the linear curvature–matter coupling given by ρ +3H (ρ + p)+ρ d ln U (ψ)+ 2V (ψ) − U (ψ)Lm ψ = 0, ds where we have introduced the Hubble function H = (1/3)∇μUμ, and we have denoted = U μ∇μ = d/ds, respectively, where ds is the line element corresponding to the metric gμν, ds2 = gμνdxμdxν
We have considered the thermodynamic interpretation of modified theories of gravity with a linear coupling between matter and geometry, which we call L f (R, Lm) gravity
Summary
In [4], the correspondence between cosmological models powered by a decaying vacuum energy density and gravitationally induced particle production was explored. The particle production cosmologies [and the associated decaying (t)-models] were modeled in the framework of field theory by a phenomenological scalar field model In this context, a new cosmic scenario with gravitationally induced particle creation was proposed [13], where the Universe evolves from an early to a late-time de Sitter era, with the recent accelerating phase driven only by the negative creation pressure associated with the CDM component. The coupling between the matter and the higher derivative curvature terms may be interpreted as an exchange of energy and momentum between the two The latter mechanism induces a gravitational particle production. 2, we present the action and the field equations of the modified gravity model with a linear curvature–matter coupling in both their standard and scalar–tensor representations.
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