Power-Law NLED-Based Magnetic Universe Can Mimic Phantom Behavior

TL;DR

This paper explores how a magnetic universe governed by non-linear electrodynamics can exhibit phantom-like behavior, influence cosmic evolution, and potentially avoid singularities and rip events, especially when considering braneworld effects.

Contribution

It introduces a class of NLED models with power-law Lagrangians that can mimic phantom fields and analyzes their cosmological implications including stability and singularity avoidance.

Findings

Magnetic fields can mimic phantom behavior depending on model parameters.

Equilibrium points suggest possible transitions from matter-dominated to inflationary phases.

Braneworld effects can prevent big bang and big rip singularities.

Abstract

We study the cosmic dynamics of a magnetic universe supported by non-linear electrodynamics (NLED) Lagrangeans that are proportional to powers of the electromagnetic invariant $\propto F^{1/(1-m)}$ ($m$ is an overall constant). For simplicity we focus in the case when $F$ depends on the magnetic field alone, a case dubbed in the bibliography as ''magnetic universe''. Our results demonstrate that, depending on the values of the free parameter $m$, the magnetic field can mimic phantom field behavior, an effect previously found in other contexts. It is demonstrated that, since there are found equilibrium points in the phase space of these models that can be associated with magnetic-dominated past and future attractors, a combination of positive and negative powers of $F$ may lead to interesting cosmological behavior. In particular, a cosmological scenario where the universe might evolve from a past NLED-driven (non-inflationary) state into a future (late-time) -- also NLED-driven -- inflationary stage, transiting through a matter-dominated solution, is envisioned. The impact of braneworld gravity on the dynamics driven by such NLED Lagrangeans is also investigated. It is demonstrated that, due to phantom property at late times, the non-linear electromagnetic effects may play an important role in deciding the fate of the cosmic evolution. Randall-Sundrum brane effects, in particular, modify the nature of the starting point of the cosmic evolution, as well as the fate of the expansion: both, the big bang singularity and the big rip event -- inherent in general relativity with phantom matter source --, may be avoided.