Narrow Results

This research delves into the study of the FRW spacetime within the framework of Chern–Simons modified gravity integrating the new Tsallis agegraphic dark energy model by examining the key cosmological parameters, including the density parameter, deceleration parameter, and equation of state. The Tsallis agegraphic dark energy model forecasts an Equation of State within the range of $(-1.20,-1.05)$ aligning well with the most recent observational data from Planck, WMAP, and BAO. The cosmic dynamics explored in this study reveal a transition from deceleration to acceleration, which is consistent with empirical observations. Density parameter graphs exhibit a shift from dark matter dominance to the prevalence of the Tsallis agegraphic model over specific redshift intervals. Furthermore, the interaction model predicts a density parameter within the range of $(-0.2,-1)$. This comprehensive inquiry offers significant insights into the impact of the $\mathrm{\Lambda }$ CDM model and quintessence on cosmic characteristics, underscoring the observed transition from a period of slowing expansion to accelerated expansion.

The early cosmic inflation, when taken along with the recent observations that the universe is currently dominated by a low density vacuum energy, leads to at least two potential problems which modern cosmology must address. First, there is the old cosmological constant problem, with a new twist: the coincidence problem. Secondly, cosmology still lacks a model to predict the observed current cosmic acceleration and to determine whether or not there is a future exit out of this state (as previously in the inflationary case). This constitutes (what is called here) a dynamical problem. Here a framework is proposed to address these two problems, based on treating the cosmic background vacuum (dark) energy as both dynamical and interacting. The universe behaves as a vacuum-driven cosmic engine which, in search of equilibrium, always back-reacts to vacuum-induced accelerations by increasing its inertia (internal energy) through vacuum energy dissipation. The process couples cosmic vacuum (dark) energy to matter to produce future-directed increasingly comparable amplitudes in these fields by setting up oscillations in the decaying vacuum energy density and corresponding sympathetic ones in the matter fields. By putting bounds on the relative magnitudes of these coupled oscillations the model offers a natural and conceptually simple channel to discuss the coincidence problem, while also suggesting a way to deal with the dynamical problem. A result with important observational implications is an equation of state w(t) which specifically predicts a variable, quasi-periodic, acceleration for the current universe. This result can be directly tested by future observational techniques such as SNAP.

We investigate the behavior of the skewness parameters for an anisotropic universe in the framework of General Relativity. Non-interacting dark energy is considered in presence of electromagnetic field. A time-varying deceleration parameter simulated by a hybrid scale factor is considered. The dynamics of the universe is investigated in presence and absence of magnetic field. The equation of state parameter of dark energy evolves within the range predicted by the observations. Magnetic field is observed to have a substantial effect on the cosmic dynamics and the skewness parameters. The models discussed here end in a big rip and become isotropic at finite time.

In this paper, we discuss a cosmological model for a universe with self-regulating features. We set up the theoretical framework for the model and determine the time evolution of the scale-factor $a(t)$. It is shown that such a universe repeatedly goes through alternate periods of matter and dark energy domination. The resulting dynamics oscillates about the would-be ideal time-linear or coasting path, with monotonic expansion. When compared to dynamics of the observed physical universe, the model recovers the observationally established evolutionary features of the latter, from the big bang to the current acceleration, and farther. It suggests a universe that initially emerges from a nonsingular state, associated with a non-exponential acceleration, and which acceleration it exits naturally with matter–energy generation. The model does not have a horizon problem or a flatness problem. It reproduces the observed current values of standard cosmic parameters, including the age $t_0$, the current Hubble parameter $H_0$ and dark energy ${\mathrm{\Omega }}_{\mathrm{\text{de}}}$ and matter ${\mathrm{\Omega }}_m$ density parameters. The model is falsifiable. It makes predictions that can be tested, as suggested. Finally, we discuss the dimensionless age $(H_0{t}_0\simeq 1)$ paradox as an example of the model’s ability to address standing puzzles. The findings suggest that dynamics of the physical universe may be self-regulating and predictable.