Cosmological tensions with non-extensive entropic cosmology: a modified stress-energy approach

Abstract We perform a comprehensive cosmographic analysis of Friedmann cosmologies modified by non-extensive entropy frameworks, focusing on Tsallis, Rényi, and Kaniadakis entropies within a novel modified energy–momentum tensor approach. In our approach the microscopic matter density remains $$\rho =m~n$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ρ</mml:mi> <mml:mo>=</mml:mo> <mml:mi>m</mml:mi> <mml:mspace/> <mml:mi>n</mml:mi> </mml:mrow> </mml:math> while the horizon thermodynamics of non-extensive entropy modifies the effective source that drives expansion, $$\rho _{eff}=f(\rho )\rho $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mrow> <mml:mi>eff</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mi>f</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>ρ</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> </mml:math> which reduces to the standard case for $$f(\rho )=1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>f</mml:mi> <mml:mo>(</mml:mo> <mml:mi>ρ</mml:mi> <mml:mo>)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:math> . By deriving the generalized Friedmann equations for each entropy type, we calculate analytical expressions for key cosmographic parameters, including the deceleration ( $$q_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>q</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> ), jerk ( $$j_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>j</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> ), snap ( $$s_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>s</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> ), and lerk ( $$l_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>l</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> ) parameters, and examine their behavior compared to the standard $$\Lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> CDM model. Our results reveal significant differences between the traditional formal approach and the modified energy–momentum approach, particularly in the Tsallis model where cosmographic parameters and the dimensionless Hubble function E ( z ) show notable deviations for deformation parameters away from unity. Moreover, both Rényi and Kaniadakis models exhibit increasing tension with $$\Lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> CDM at higher redshifts, while remaining similar at low redshifts. Importantly, given the persistent $$\sim 5\sigma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>5</mml:mn> <mml:mi>σ</mml:mi> </mml:mrow> </mml:math> Hubble tension between local and global measurements, our analysis indicates that the flexibility of the modified entropic cosmology framework to alter the expansion rate could potentially alleviate this discrepancy by modifying the effective expansion history in a way compatible with observations. Future work will involve full Bayesian analyses with Pantheon+, DESI, and Planck data to further assess the viability of these models in resolving current cosmological tensions.