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

Abstract

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.

Figures (6)

• Figure 1: Timeline of the complete cosmological scenario from the initial Sitter ($H_I$) to a final Sitter ($H_F$) stage (out of visual scale). Immediately after the unknown primordial quantum gravity state, ultra relativistic particles and radiation are created at the expenses of gravity (curvature) with the rate $\Gamma_I=3H_I$ and inflate the cosmos. Inflation ends ($\ddot a=0$) for $H=H_e$, when the decelerating radiation dominated (RD) phase begins ($\ddot a<0$). This RD regime with creation ends at $z=z_{eq}$ marking the begin of the decelerating matter dominated (MD) phase with creation. At $z_{t}$, the creation pressure accelerates the cosmic expansion once more, which is observed today ($z=0$), until it finally induces a final de Sitter-like stage powered by $\Gamma_F=3H_F$ in the very distant future. Figure adapted from PLS2024.
• Figure 2: The evolution of the deceleration parameter (\ref{['qzab']}) with respect to the redshift $z$. Figure a) depicts the evolution of $q(z)$ for different values of $\alpha$ with $\beta=0$. Figure b) represents the changes in the evolution of $q(z)$ caused by the contributions of different values of $\beta$ considering $\alpha=0.7$ (value predicted by the CCDM model). In both plots the predictions of the $\Lambda$CDM model (empty black circles) coincides with the CCDM model (yellow lines, $\alpha=0.7,\beta=0$).
• Figure 3: Constraints on $M$, $H_0$, $\alpha$, $\beta$, using SNe Ia observations and Cepheid calibrations from the Pantheon+SH0ES compilation Brout2022, along with $H(z)$ data from cosmic chronometers MorescoEtAl20MorescoEtAl22.
• Figure 4: The Likelihood of the transition redshift $z_t$, regarding the constraints on the parameters $\alpha$ and $\beta$ from the compilation Pantheon+SH0ES Brout2022 with $H(z)$ CC data MorescoEtAl20MorescoEtAl22 and the theoretical prediction for $z_t$ in equation (\ref{['zt_ab']}), which constrains $z_t$ to $z_t=0.917^{+0.0070+0.67}_{-0.31-0.38}$ at 1$\sigma$ and $2\sigma$ c.l.
• Figure 5: Combined constraints on $M$, $H_0$, $\alpha$, $\beta$, using the datasets Pantheon+SH0ES Brout2022 and $H(z)$ from cosmic chronometers (CC) MorescoEtAl20MorescoEtAl22.