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Negative cosmological constant in the dark sector?
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abstract
We consider the possibility that the dark sector of our Universe contains a negative cosmological constant dubbed $\lambda$. For such models to be viable, the dark sector should contain an additional component responsible for the late-time accelerated expansion rate ($X$). We explore the departure of the expansion history of these models from the concordance $\Lambda$ Cold Dark Matter model. For a large class of our models the accelerated expansion is transient with a nontrivial dependence on the model parameters. All models with $w_X>-1$ will eventually contract and we derive an analytical expression for the scale factor $a(t)$ in the neighborhood of its maximal value. We find also the scale factor for models ending in a Big Rip in the regime where dustlike matter density is negligible compared to $\lambda$. We address further the viability of such models, in particular when a high $H_0$ is taken into account. While we find no decisive evidence for a nonzero $\lambda$, the best models are obtained with a phantom behavior on redshifts $z\gtrsim 1$ with a higher evidence for nonzero $\lambda$. An observed value for $h$ substantially higher than $0.70$ would be a decisive test of their viability.
Forward citations
Cited by 5 Pith papers
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Alleviating the Hubble Tension with Smooth Sign-Switching Dark Energy: Full CMB Constraints with DESI and PantheonPlus
Smooth ECDM dark energy remains compatible with Planck+ACT+SPT, DESI DR2 and Pantheon+/SH0ES while alleviating the Hubble tension through a controlled late-time density transition.
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Background-level reconstruction of scalar-field potentials from dark-energy histories and comparison with analytic potential families
A background reconstruction maps prescribed ρ_de(z) histories to V(φ) and ranks analytic potentials by Bayesian evidence, with exponential preferred for CPL and shifted-tanh for sign-switching targets.
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Can the universe experience an AdS landscape since matter-radiation equality?
A universe with an AdS (negative cosmological constant) phase at recombination and another at low redshift is compatible with Planck, DESI, Pantheon Plus and SH0ES data, though not preferred by them.
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The Lifespan of our Universe
If the axion dark energy model with a negative cosmological constant is the true explanation of DES/DESI data, the universe will end in a big crunch at a total age of about 33 billion years.
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