Singularity-Free Emergent Universe from Non-Conventional Matter: Observational Viability of New Late-Time Dynamics

We investigate a viable realization of the emergent universe paradigmwithin standard relativistic cosmology, supported by an extended Chaplygingas that generalizes the modified Chaplygin gas through the inclusion of higher-order barotropic corrections. Restricting ourselves to aquadratic extension of the equation of state, we demonstrate that this effectivefluid can simultaneously account for late-time cosmic acceleration and serve as a plausible dark energy candidate. Assuming dominance ofthis fluid at late epochs, we construct an emergent universe model thatnaturally avoids an initial singularity in a spatially flat background anddeparts from the conventional ΛCDM expansion history. The resultingcosmological evolution exhibits distinctly non-standard late-time behavior:the effective dark energy component crosses the phantom divide in both the past and the present, transitions into a thawing regime in thefuture, and asymptotically evolves toward a decelerating phase, renderingdark energy a transient phenomenon rather than a permanent driver of acceleration. Model parameters are constrained using Markov ChainMonte Carlo analyses with Pantheon supernova and observational Hubbledata, and the inferred evolution of key cosmological observables is foundto qualitatively resemble recent DESI results. Notably, the model providesan improved fit to the observed Hubble parameter at redshift z = 2.34 aswell as to the present value of the Hubble constant when compared to the ΛCDM framework, a comparison that is placed on a firmer statistical footing through minimum χ 2 , AIC and BIC diagnostics (Sec. 3.3). These findings indicate that the extended Chaplygingas not only offers a viable description of dark energy but also supportsan emergent universe scenario unlike the modified Chaplygin gas, therebyresolving the initial singularity problem in a flat universe within the standard relativistic context.