P. W. R. Lima | Searcharxiv

arXiv2025

Cosmic Expansion Driven by Gravitational Particle Production: Toward a Complete Cosmological Scenario

A dark-energy-free cosmological model ($Ω_{DE} \equiv 0$) based on gravitationally induced adiabatic particle creation is proposed. The thermodynamics of particle production yields an effective negative pressure that drives both primordial inflation and late-time cosmic acceleration. The model, characterized by four components and two free parameters ($α$, $β$), reproduces a $Λ$CDM-like expansion for suitable $α$, while $β$ introduces small but testable deviations from the cosmic concordance model. Constraints from type Ia Supernovae (Pantheon+SH0ES) and H(z) data indicate $β\simeq 0.13$, suggesting a mild departure from standard cosmology and possible relief of the $H_0$ and $S_8$ tensions. The resulting classical cosmology evolves smoothly between two extreme de Sitter phases, offering a singularity-free, unified scenario that beyond solving old cosmological puzzles opens a new perspective to handle the tensions plaguing the current cosmic concordance model.

astro-ph.CO↗

arXiv2025

New accelerating cosmology without dark energy: The particle creation approach and the reduced relativistic gas

The standard procedure to explain the accelerated expansion of the Universe is to assume the existence of an exotic component with negative pressure, generically called dark energy. Here, we propose a new accelerating flat cosmology without dark energy, driven by the negative creation pressure of a reduced relativistic gas (RRG). When the hybrid dark matter of the RRG is identified with cold dark matter, it describes the so-called CCDM cosmology whose dynamics is equivalent to the standard $Λ$CDM model at both the background and perturbative levels (linear and nonlinear). This effect is quantified by the creation parameter $α$. However, when the pressure from the RRG slightly changes the dynamics of the universe, as measured by a parameter $b$, the model departs slightly from the standard $Λ$CDM cosmology. Therefore, this two-parametric model ($α, b$) describes a new scenario whose dynamics is different but close to the late-time scenarios predicted by CCDM and $Λ$CDM models. The free parameters of the RRG model with creation are constrained based on SNe Ia data (Pantheon+SH0ES) and also using $H(z)$ from cosmic clocks. In principle, this mild distinction in comparison with both CCDM or $Λ$CDM may help alleviate some cosmological problems plaguing the current standard cosmology.

astro-ph.CO↗