Vacuum stability of phantom field from the nonuniqueness of Lagrangian

TL;DR

This paper explores how the nonuniqueness of scalar field Lagrangians can lead to a bounded energy density for phantom fields, impacting their stability and cosmological implications.

Contribution

It introduces a new approach using linear combinations of Lagrangians to analyze vacuum stability in phantom fields.

Findings

Energy density of phantom fields can be bounded from below.

New Lagrangian formulations relate to ghost condensate behavior.

Implications for equations of state with w<-1.

Abstract

According to the nonuniqueness principle, the homogeneous scalar field Lagrangian can be expressed in various forms both standard and nonstandard ones. Therefore, the standard and all possible nonstandard Lagrangians can be linearly combined while the Klein-Gordon equation is still intact. This linear combination of Lagrangians is used to demonstrate that the energy density of homogeneous phantom field can possibly be bounded from below. The applications of this new Lagrangian in the nature of the ghost condensate and the equation of state with $w<-1$ are discussed.