In this work we explore a new cosmological solution for an universe filled with one dissipative fluid, described by a barotropic equation of state (EoS) $p=\omega \rho$, in the framework of the full Israel-Stewart theory. The form of the bulk viscosity has been assumed of the form $\xi ={\xi }_0{\rho }^{1/2}$. The relaxation time is taken to be a function of the EoS, the bulk viscosity and the speed of bulk viscous perturbations, $c_b$. The solution presents an initial singularity, where the curvature scalar diverges as the scale factor goes to zero. Depending on the values for $\omega$, ${\xi }_0$, $c_b$ accelerated and decelerated cosmic expansion can be obtained. In the case of accelerated expansion, the viscosity drives the effective EoS to be of quintessence type, for the single fluid with positive pressure. Nevertheless, we show that only the solution with decelerated expansion satisfies the thermodynamics conditions $dS/dt>0$ (growth of the entropy) and $d^{2}S/d{t}^2<0$ (convexity condition). We show that an exact stiff matter EoS is not allowed in the framework of the full causal thermodynamic approach; and in the case of a EoS very close to the stiff matter regime, we found that dissipative effects becomes negligible so the entropy remains constant. Finally, we show numerically that the solution is stable under small perturbations.

We perform a study both statistical and theoretical for cosmological models of matter creation and their ability to describe effective phantom models of dark energy. Such models are beyond the $\mathrm{\Lambda }\mathrm{CDM}$ model since the resulting cosmic expansion is not adiabatic. In fact, we show that this approach exhibits transient phantom/quintessence scenarios at present time and tends to the standard cosmological model at some stage of the cosmic evolution. We discuss some generalities of the thermodynamics properties for this type of cosmological model; we emphasize on the behavior of the temperature associated to dark matter, which keeps positive along cosmic evolution together with the entropy. The enrichment of this type of model by means of the incorporation of cosmological constant and dissipative effects in the fluid description to explore their cosmological consequences in the expansion of the Universe is considered. Finally, a generalization for the matter production rate as an inhomogeneous expression of the Hubble parameter and its derivatives is discussed; as in all the cases examined, such election leads to an effective phantom/quintessence behavior.

In this work, we present an analysis of the phantom zone in a causal viscous cosmology from a thermodynamic point of view. In this description, we consider a chemical potential and the approach of irreversible processes. We assume a flat universe filled with a single dissipative fluid described by a barotropic equation of state, $p=\omega \rho$. This model allows us to construct a negative chemical potential for the phantom regime and have positive definite temperature and entropy.

In this work, we study some thermodynamical aspects associated with torsion in a flat FLRW spacetime cosmic evolution. By implementing two Ansatze for the torsion term, we find that the model admits a phantom regime or a quintessence behavior. This scheme differs from the $$\Lambda $$Λ CDM model at the thermodynamical level. The resulting cosmic expansion is not adiabatic, the fulfillment of the second law of thermodynamics requires a positive torsion term, and the temperature of the cosmic fluid is always positive. The entropy of the torsion phantom scenario is negative, but introducing chemical potential solves this issue. For a Dirac-Milne type Universe, the torsion leads to a growing behavior for the temperature of the fluid but has no incidence on the rate of expansion.

We explore the cosmological implications at effective level of matter creation effects in a dissipative fluid for a Friedmann-Lemaitre-Robertson-Walker geometry; we also perform a statistical analysis for this kind of model. By considering an inhomogeneous ansatz for the particle production rate, which we obtain for a created matter of dark matter type, we can have a quintessence scenario or a future singularity known as a little rip; this is in dependence of the value of a constant parameter, $\eta$, which characterizes the matter production effects. The dimensionless age of this kind of universe is computed, showing that this number is greater than the standard cosmology value; this is typical of universes with the presence of dark energy. The inclusion of baryonic matter is studied. We implement the construction of the particle production rate for a dissipative fluid by considering two approaches for the expression of the bulk viscous pressure: we find that, in the Eckart model, we have a big rip singularity leading to a catastrophic matter production, and in the truncated version of the Israel-Stewart model this rate remains bounded, which leads to a quintessence scenario. For a nonadiabatic dissipative fluid, we obtain a positive temperature, and the cosmic expansion obeys the second law of thermodynamics.