Varying Speed Of Light Theories Research Articles

Bianchi Type I Cosmological Model with Viscous Fluid in the Framework of VSL Theory

The Bianchi type I cosmological model in the framework of Variable Speed of Light (VSL) theory is investigated, by taking into account the effect due to viscosity, considering \(\overline{p}= p-3\zeta H\) where \(\zeta = \zeta_0 \rho H^{-1}\). The Einstein field equations are solved for variable \(G\), \(c\) and \(\Lambda\) in which \(G\), \(c\), \(\Lambda\) and shear parameter \(\sigma^{2}\), all are coupled. It is shown that the viscosity term exhibits the influence on the form of solutions, in the framework of varying speed of light theory.

Temporally varying universal gravitational “constant” and speed of light in energy momentum squared gravity

Energy Momentum Squared Gravity (EMSG) is a cosmological model where the scale factor is non vanishing at all times and hence does not favor big bang cosmology. However, the profile of density in the radiation dominated universe shows that EMSG supports inflationary cosmology. Inflationary cosmological models are successful in providing convincing answers to major cosmological issues like horizon problem, flatness problem and small value of cosmological constant but hitherto no model of inflation has been observationally confirmed. Owing to this, Varying Speed of Light (VSL) were introduced which are a class of cosmological models which disfavor inflation and propose an alternative route to solve these cosmological issues by just allowing the speed of light (and Newtonian Gravitational constant) to vary. VSL theories were motivated to address the shortcomings of inflation but do not address the shortcomings related to the initial big bang singularity. In this spirit, we present here a novel cosmological model which is free from both the "initial big bang singularity" and "inflation" by incorporating a mutually varying speed of light $c(t)$ and Newtonian gravitational constant $G(t)$ in the framework of EMSG. We report that in EMSG, for a dust universe ($\omega=0$), cosmological models for a time varying $c(t)$ and $G(t)$ and constant $c$ and $G$ are indistinguishable, whereas for a radiation dominated universe ($\omega = 1/3$), a mutually varying $c(t)$ and $G(t)$ provides an exiting alternative to inflationary cosmology which is also free from initial big bang singularity. We further report that for an ansatz of scale factor representing a bouncing cosmological model, the VSL theory can be applied to a quadratic $T$ gravity model to get rid of "inflation" and "big bang singularity" and concurrently solve the above mentioned cosmological enigmas.

Statistical Hierarchy of Varying Speed of Light Cosmologies

Abstract Many varying speed of light (VSL) theories have been developed recently. Here we address the issue of their observational verification in a fully comprehensive way. By using the most updated cosmological probes, we test three different candidates for a VSL theory (Barrow & Magueijo, Avelino & Martins, and Moffat). We consider many different Ansätze for both the functional form of c(z) and the dark energy dynamics. We compare these results using a reliable statistical tool such as the Bayesian evidence. We find that the present cosmological data are perfectly compatible with any of these VSL scenarios, but for the Moffat model there is a higher Bayesian evidence ratio in favor of VSL rather than the c = constant ΛCDM scenario. Moreover, in such a scenario, the VSL signal can help to strengthen constraints on the spatial curvature (with indication toward an open universe), to clarify some properties of dark energy (exclusion of a cosmological constant at level), and is also falsifiable in the near future owing to peculiar issues that differentiate this model from the standard one. Finally, we apply an information prior and entropy prior in order to put physical constraints on the models, though still in favor Moffat’s proposal.

Bianchi type i cosmological model with varying G, Λ & σ2 in VSL theory

In this paper we study the Bianchi type I cosmological model in the framework of variable speed of light (VSL) theory. The cosmological field equations are solved for variable G，c and Λ coupled with shear parameter σ2. It is shown for the large value of t the resulting model reduces to FLRW model with Λ approaches to constant. We also derived exact expressions for the look back time, proper distance, luminosity distance and angular diameter distance versus redshift in the framework of VSL theory as already discussed by Khadekar and Kamdi [Int. Jour. Theo. Phys. 48 314% (2009)] in differ­ent context.

SNe data analysis in variable speed of light cosmologies without cosmological constant

In this work, we aim to show the possibilities of the variable speed of light (VSL) theory in explaining the type Ia supernovae (SNe) observations without introducing dark energy. The speed of light is assumed to be scale factor-dependent, which is the most popular assumption in VSL theory. We show the modified calculation of the distance modulus and the validity of the redshift-scale factor relation in VSL theory. Three different models of VSL are tested SNe data-sets with proper constraints on the model parameters. The comparison of the three models and flat ΛCDM in distance modulus is showed. Some basic problems and the difficulties of the confirmation of the VSL theory are also discussed.

Calculating the Exact Experimental Density of the Dark Energy in the Cosmos Assuming a Fractal Speed of Light

Fractal speed of light theory is a variation of Magueijo-Smolin varying speed of light (VSL) theoretical modification of Einstein’s energy mass relation. We use this theory to derive an exact value for the missing dark energy which is found to be in astonishing agreement with the latest result of the WMAP measurement and the independent supernova analysis. Thus while Einstein’s formula predicts 95.5% more energy than found in highly precise astrophysical measurement, our VSL- based calculation indicates an exact theoretical value of only 4.508497% real energy. Consequently, the exact conjectured missing dark energy must be 95.491502%. By any standards, this is an astounding confirmation for both the cosmological measurement and the VSL theory.

A phenomenological variable speed of light theory and the secular increase of the astronomical unit

A phenomenological variable speed of light theory and the secular increase of the astronomical unit

Thermodynamics in Variable Speed of Light Theories

Variable speed of light theories (VSL) are interesting because they could solve several cosmological puzzles. In this work we study the thermodynamics and Newtonian limit of the varying speed of light theory developed by J. Magueijo (Magueijo 2000). In the covariant and locally Lorentz invariant VSL proposed by Magueijo c is a dimensionless dynamical scalar field c=c0eψ, where c0 is a constant. The matter and gravitational lagrangians are multiplied by the factors ebψ and eaψ respectively.

Thermodynamics in variable speed of light theories

The perfect fluid in the context of a covariant variable speed of light theory proposed by J. Magueijo is studied. On the one hand the modified first law of thermodynamics together with a recipe to obtain equations of state are obtained. On the other hand the Newtonian limit is performed to obtain the nonrelativistic hydrostatic equilibrium equation for the theory. The results obtained are used to determine the time variation of the radius of Mercury induced by the variability of the speed of light ($c$), and the scalar contribution to the luminosity of white dwarfs. Using a bound for the change of that radius and combining it with an upper limit for the variation of the fine structure constant, a bound on the time variation of $c$ is set. An independent bound is obtained from luminosity estimates for Stein 2015B.

Bimetric varying speed of light theories and primordial fluctuations

We exhibit a varying speed of light (VSL) theory that implements the recently proposed decaying speed of sound mechanism for generating density fluctuations. We avail ourselves of bimetric VSL theories, where the speed of gravity differs from that of light. We first show that a Dirac-Born-Infeld (DBI) type of $K$-essence has the necessary speed of sound profile to produce (near) scale-invariant fluctuations. We then examine the map between bimetric and $K$-essence models: typically the bi-scalar connecting the two metrics is a $K$-essence field in one of them. Remarkably, the DBI model is found to perturbatively represent the minimal bimetric model, where the bi-scalar is Klein-Gordon in the matter frame. But the full non-perturbative bimetric structure is even simpler: the bi-scalar dynamics should be simply driven by a cosmological constant in the matter frame, balanced by an opposite cosmological constant in the gravity frame. Thus the problem of structure formation receives an elegant and universal solution within bimetric VSL theories, which are known to also solve the flatness and entropy problems and evade a plethora of causality concerns.

Unusual features of varying speed of light cosmologies

We contrast features of simple varying speed of light (VSL) cosmologies with inflationary universe models. We present new features of VSL cosmologies and show that they face problems explaining the cosmological isotropy problem. We also find that if c falls fast enough to solve the flatness and horizon problems then the quantum wavelengths of massive particle states and the radii of primordial black holes can grow to exceed the scale of the particle horizon. This may provide VSL cosmologies with a self-reproduction property. The constraint of entropy increase is also discussed. The new problems described in the this Letter provide a set of bench tests for more sophisticated VSL theories to pass.

COSMOLOGY 'WITHOUT' CONSTANTS

We review varying speed of light (VSL) theories, in a cosmological and astrophysical setting, and as phenomenological descriptions of quantum gravity. We first introduce two observational puzzles, and explain how they may related to VSL. We then catalogue the various theoretical efforts associated with VSL. We focus on recent VSL theories rendering the Planck energy invariant, and capable of explaining the unwarranted existence of ultra high energy cosmic rays. We conclude highlighting the main shortcoming of current VSL theories: structure formation; and present directions in which it may be addressed.

Is it e or is it c? Experimental tests of varying alpha

Is the recent evidence for a time-varying fine structure ‘constant’ α to be interpreted as a varying e, c, ℏ, or a combination thereof? We consider the simplest varying electric charge and varying speed of light (VSL) theories and prove that for the same type of dark matter they predict opposite senses of variation in α over cosmological times. We also show that unlike varying e theories, VSL theories do not predict violations of the weak equivalence principle (WEP). Varying e theories which explain astronomical inferences of varying α predict WEP violations only an order of magnitude smaller than existing Eötvös experiment limits but could be decisively tested by STEP. We finally exhibit a set of atomic-clock and related experiments for which all (hyperbolic) varying α theories predict non-null results. They provide independent tests of the recent astronomical evidence.

Variable Speed of Light Theories

Two variable speed of light models and their physical consequences are investigated.