Unifying phantom inflation with late-time acceleration: scalar phantom-non-phantom transition model and generalized holographic dark energy

TL;DR

The paper addresses unifying early-time phantom inflation with late-time phantom acceleration. It presents two complementary approaches: a scalar-tensor model with a kinetic coupling and a generalized holographic dark energy framework whose infrared cutoff is $L_\Lambda$ depending on FRW quantities. In the scalar model, explicit toy constructions show smooth phantom–non-phantom transitions and, in a two-field variant, finite stability eigenvalues at the crossing, supporting a unified phantom evolution. In the holographic model, phantom crossing can occur, matter coupling can address the coincidence problem, and a holographic entropy bound plus a Cardy-Verlinde relation $S_H^2=(2\pi L_\Lambda)^2 E_c (E_c+E_m)$ is obtained, suggesting a viable route to unify phantom inflation with phantom acceleration.

Abstract

The unifying approach to early-time and late-time universe based on phantom cosmology is proposed. We consider gravity-scalar system which contains usual potential and scalar coupling function in front of kinetic term. As a result, the possibility of phantom-non-phantom transition appears in such a way that universe could have effectively phantom equation of state at early time as well as at late time. In fact, the oscillating universe may have several phantom and non-phantom phases. As a second model we suggest generalized holographic dark energy where infrared cutoff is identified with combination of FRW parameters: Hubble constant, particle and future horizons, cosmological constant and universe life-time (if finite). Depending on the specific choice of the model the number of interesting effects occur: the possibility to solve the coincidence problem, crossing of phantom divide and unification of early-time inflationary and late-time accelerating phantom universe. The bound for holographic entropy which decreases in phantom era is also discussed.