Varying vacuum energy of a self-interacting scalar field

TL;DR

This paper proposes a mechanism where the vacuum energy of a self-interacting scalar field varies naturally during cosmic evolution, potentially explaining the decreasing cosmological constant and suggesting a cyclic universe scenario.

Contribution

It introduces a novel mechanism showing how interaction affects the number of field modes, leading to a natural variation in vacuum energy without additional assumptions.

Findings

Vacuum energy can vary between maximum and zero due to interactions.

During inflation, the scalar field transitions to a state with reduced vacuum energy.

The current cosmological constant is predicted to decrease, supporting a cyclic universe model.

Abstract

Understanding mechanisms capable of altering the vacuum energy is currently of interest in field theories and cosmology. We consider an interacting scalar field and show that the vacuum energy naturally takes any value between its maximum and zero because interaction affects the number of operating field modes, the assertion that involves no assumptions or postulates. The mechanism is similar to the recently discussed temperature evolution of collective modes in liquids. The cosmological implication concerns the evolution of scalar field $\phi$ during the inflation of the Universe. $\phi$ starts with all field modes operating and maximal vacuum energy in the early inflation-dominated epoch. As a result of inflation, $\phi$ undergoes a dynamical crossover and arrives in the state with one long-wavelength longitudinal mode and small positive vacuum energy predicted to be asymptotically decreasing to zero in the late epoch. Accordingly, we predict that the currently observed cosmological constant will decrease in the future, and comment on the possibility of a cyclic Universe.