Quintessence-dominated cyclic universe with negative cosmological constant

TL;DR

This paper explores two simplified cyclic universe models with a negative, time-varying cosmological constant, demonstrating physically acceptable evolutions and novel pressure sign-flipping phenomena without violating energy conditions.

Contribution

It introduces two non-singular cyclic models with negative cosmological constant, showing sign-flipping of pressure and crossing of the phantom divide line in a matter-bounce scenario.

Findings

Positive energy density evolution is achievable with negative cosmological constant.

Sign flipping of cosmic pressure occurs without violating null energy condition.

The models exhibit crossing of the phantom divide line near the bounce.

Abstract

We investigate two simplified non-singular cyclic models with a negative time-varying cosmological constant to represent the non-conventional mechanism of negative cosmological constant expected to address the late-time cosmic acceleration. We show that a physically acceptable evolution with positive energy density can be realized, while negative energy density dominates in case of a positive or zero cosmological constant. In the first model, we demonstrate a sign flipping of the cosmic pressure in a quintessence-dominated universe with no violation of the null energy condition. In the second model, we propose a matter-bounce scenario with showing the crossing of the phantom divide line in the vicinity of the bounce. We find that while we get positive kinetic term and scalar potential, the sum of scalar and quantum potentials is negative.