A Spectrum of Cosmological Rips and Their Observational Signatures

Abstract

We present a unified dark energy framework capable of generating a continuous spectrum of cosmological ``rip'' scenarios -- including the Big Rip, Grand Rip, Mild Rip, Little Rip, Little Sibling of the Big Rip, and the newly found Dollhouse Rip -- while ensuring a physically consistent evolution across cosmic history. Building on earlier phenomenological proposals, we introduce a barotropic equation-of-state parameter with a sigmoid-like correction to guarantee a strictly positive dark energy density and to avoid early-time pathologies commonly present in previous models. Using this formulation, closed-form analytic expressions for the energy density can be obtained. This, in turn, enables a systematic classification of future singularities based on the signs and magnitudes of two key parameters of the model. We test these scenarios with state-of-the-art cosmological probes, including DESI DR2 BAO, cosmic chronometers, CMB compressed likelihoods, and the Pantheon+ supernovae sample. According to our Bayesian analysis, all rip scenarios yield best-fit parameters compatible with $\Lambda$CDM at the $1\sigma$ level, with Bayes factors weakly favoring $\Lambda$CDM. The mild, logarithmic evolution of the proposed dark energy density prevents current observations from distinguishing among the different future fates. We conclude that, for rip cosmologies to gain observational support over $\Lambda$CDM, they must display more accentuated late-time dynamical features -- such as perhaps rapid transitions or a phantom-divide crossing -- within the redshift range probed by present surveys.

V1: 12 pages, 1 figure

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