A Spectrum of Cosmological Rips and Their Observational Signatures

TL;DR

This work proposes a unified dark energy framework with a sigmoid-like correction to the EOS that guarantees $\rho>0$ and analytic evolution, enabling a cascade of future cosmological rips (including the Big Rip, Grand Rip, Mild Rip, Little Rip, Little Sibling of the Big Rip, and the Dollhouse Rip) controlled by parameters $\alpha$ and $n$. The authors derive a closed-form DE density $\rho(a)$ and analyze asymptotic behaviors, classifying possible fates and their associated $H(t)$ behavior and derivatives. They confront the model with current data (DESI DR2 BAO, cosmic chronometers, CMB compressed likelihoods, Pantheon+ SN) in a Bayesian framework, finding all rip cases statistically compatible with $\Lambda$CDM at $1\sigma$, with Bayes factors weakly favoring $\Lambda$CDM due to the slow logarithmic DE evolution. The results suggest that, to observationally favor rip cosmologies over $\Lambda$CDM, more pronounced late-time dynamics or phantom-divide crossing within accessible redshift ranges would be required. Overall, the paper provides a robust, theoretically well-behaved route to explore a spectrum of cosmic destinies while remaining consistent with current observational constraints.

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 $Λ$CDM at the $1σ$ level, with Bayes factors weakly favoring $Λ$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 $Λ$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.

Figures (1)

• Figure 1: One-dimensional marginalized and normalized posterior distributions of $\alpha$ for $n = 1/3$. As the results for $\alpha$ are almost $n$-independent, similar distributions follow for other rip scenarios. Datasets are combined into early- (CMB+BAO) or late-time (SN+CC) observables.