Analogue gravity is a research programme which investigates analogues of
general relativistic gravitational fields within other physical systems,
typically but not exclusively condensed matter systems, with the aim of gaining
new insights into their corresponding problems Analogue models of (and for)
gravity have a long and distinguished history dating back to the earliest years
of general relativity In this review article we will discuss the history,
aims, results, and future prospects for the various analogue models We start
the discussion by presenting a particularly simple example of an analogue
model, before exploring the rich history and complex tapestry of models
discussed in the literature The last decade in particular has seen a
remarkable and sustained development of analogue gravity ideas, leading to some
hundreds of published articles, a workshop, two books, and this review article
Future prospects for the analogue gravity programme also look promising, both
on the experimental front (where technology is rapidly advancing) and on the
theoretical front (where variants of analogue models can be used as a
springboard for radical attacks on the problem of quantum gravity)

Analogue Gravity

Quintom Cosmology: theoretical implications and observations

A Critical Review of Classical Bouncing Cosmologies

We consider several new classes of viable vector field alternatives to the inflaton and quintessence scalar fields. Spatial vector fields are shown to be compatible with the cosmological anisotropy bounds if only slightly displaced from the potential minimum while dominant, or if driving an anisotropic expansion with nearly vanishing quadrupole today. The Bianchi I model with a spatial field and an isotropic fluid is studied as a dynamical system, and scaling solutions of several types are found. On the other hand, time-like fields are automatically compatible with large-scale isotropy. We show that they can be dynamically important if non-minimal gravity couplings are taken into account. We reconstruct as an example a vector–Gauss–Bonnet model which generates the concordance model acceleration at late times and supports an inflationary epoch at high curvatures. The evolution of the vortical perturbations in such models is computed.

Vector field models of inflation and dark energy

There is evidence that Newton and Einstein's theories of gravity cannot explain the dynamics of a universe made up solely of baryons and radiation. To be able to understand the properties of galaxies, clusters of galaxies and the universe on the whole it has become commonplace to invoke the presence of dark matter. An alternative approach is to modify the gravitational field equations to accommodate observations. We propose a new class of gravitational theories in which we add a new degree of freedom, the Aether, in the form of a vector field that is coupled covariantly, but nonminimally, with the space-time metric. We explore the Newtonian and non-Newtonian limits, discuss the conditions for these theories to be consistent and explore their effect on cosmology.

Modifying gravity with the aether : An alternative to dark matter

It is shown that the addition of a nonlinear term to the Lagrangian of the electromagnetic field yields a fluid with an asymptotically super-negative equation of state, causing an accelerated expansion of the Universe. Some general properties of nonlinear electromagnetism in cosmology are also discussed.

https://arxiv.org/pdf/astro-ph/0312093.pdf

Nonlinear electrodynamics and the acceleration of the Universe

Maxwell electrodynamics, considered as a source of the classical Einstein field equations, leads to the singular isotropic Friedmann solutions. We show that this singular behavior does not occur for a class of nonlinear generalizations of the electromagnetic theory. A mathematical toy model is proposed for which the analytical nonsingular extension of FRW solutions is obtained.

Nonlinear electrodynamics and FRW cosmology

It will be shown that a given realization of nonlinear electrodynamics, used as a source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way of solving two important problems in cosmology.

Cosmological effects of nonlinear electrodynamics

We study here some consequences of the nonlinearities of the electromagnetic field acting as a source of Einstein's equations on the propagation of photons. We restrict to the particular case of a `regular black hole', and show that there exist singularities in the effective geometry. These singularities may be hidden behind a horizon or be naked, according to the value of a parameter. Some unusual properties of this solution are also analysed.

https://iopscience.iop.org/article/10.1088/0264-9381/17/18/316/pdf

Singularities in General Relativity coupled to nonlinear electrodynamics

We show that a flowing dielectric medium with a linear response to an external electric field can be used to generate an analogue geometry that has many of the formal properties of a Schwarzschild black hole for light rays, in spite of birefringence. The surface gravity of this analogue black hole has a contribution that depends only on the dielectric properties of the fluid (in addition to the usual term dependent on the acceleration). This term may give a hint at a new mechanism to increase the temperature of Hawking radiation.

J. M. Salim

Papers

Nonlinear electrodynamics and the acceleration of the Universe

Nonlinear electrodynamics and FRW cosmology

Cosmological effects of nonlinear electrodynamics

Singularities in General Relativity coupled to nonlinear electrodynamics

Analogue black holes in flowing dielectrics