The final state and thermodynamics of dark energy universe

TL;DR

This work analyzes the fate of dark-energy–dominated universes with phantom-like equations of state and demonstrates that quantum backreaction from the conformal anomaly can dominate near would-be future singularities. By constructing scalar-tensor models that exhibit sudden futures and incorporating $ ho_A$ and $p_A$ feedback, the authors show that the Big Rip can be moderated or avoided, often steering the cosmos toward a de Sitter-like end state. They further study thermodynamics and entropy bounds, finding that quantum corrections render entropies finite and modify the evolution of black hole masses in phantom backgrounds. Collectively, the results suggest phantom-driven futures are transient and that quantum-gravity effects can restore a stable, inflationary-like late-time expansion with well-defined thermodynamic bounds.

Abstract

As it follows from the classical analysis, the typical final state of the dark energy universe where dominant energy condition is violated is finite time, sudden future singularity (Big Rip). For a number of dark energy universes (including scalar phantom and effective phantom theories as well as specific quintessence model) we demonstrate that quantum effects play the dominant role near Big Rip, driving the universe out of future singularity (or, at least, making it milder). As a consequence, the entropy bounds with quantum corrections become well-defined near Big Rip. Similarly, black holes mass loss due to phantom accretion is not so dramatic as it was expected: masses do not vanish to zero due to transient character of phantom evolution stage. Some examples of cosmological evolution for negative, time-dependent equation of state are also considered with the same conclusions. The application of negative entropy (or negative temparature) occurence in the phantom thermodynamics is briefly discussed.