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Register a new userA statefinder luminosity distance formula in varying speed of light cosmology
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Mariusz Dabrowski P.
Publication date
2014
fields
Physics
and research's language is
English
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We derive a luminosity distance formula for the varying speed of light (VSL) theory which involves higher order characteristics of expansion such as jerk, snap and lerk which can test the impact of varying $c$ onto the evolution of the universe. We show that the effect of varying $c$ is possible to be isolated due to the relations connecting observational parameters already by measuring the second-order term in redshift $z$ unless there is a redundancy between the curvature and an exotic fluid of cosmic strings scaling the same way as the curvature.
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In this letter we describe a new method to use Baryon Acoustic Oscillations (BAO) to derive a constraint on the possible variation of the speed of light. The method relies on the fact that there is a simple relation between the angular diameter distance $(D_{A})$ maximum and the Hubble function $(H)$ evaluated at the same maximum-condition redshift, which includes speed of light $c$. We note the close analogy of the BAO probe with a laboratory experiment: here we have $D_{A}$ which plays the role of a standard (cosmological) ruler, and $H^{-1}$, with the dimension of time, as a (cosmological) clock. We evaluate if current or future missions such as Euclid can be sensitive enough to detect any variation of $c$.
It has been recently claimed that cosmologies with time dependent speed of light might solve some of the problems of the standard cosmological scenario, as well as inflationary scenarios. In this letter we show that most of these models, when analyzed in a consistent way, lead to large violations of charge conservation. Thus, they are severly constrained by experiment, including those where $c$ is a power of the scale factor and those whose source term is the trace of the energy-momentum tensor. In addition, early Universe scenarios with a sudden change of $c$ related to baryogenesis are discarded.
The phantom brane has several important distinctive features: (i) Its equation of state is phantom-like, but there is no future `big rip singularity, (ii) the effective cosmological constant on the brane is dynamically screened, because of which the expansion rate is {em smaller} than that in $Lambda$CDM at high redshifts. In this paper, we constrain the Phantom braneworld using distance measures such as Type Ia supernovae (SNeIa), Baryon Acoustic Oscillations (BAO), and the compressed Cosmic Microwave Background (CMB) data. We find that the simplest braneworld models provide a good fit to the data. For instance, BAO +SNeIa data can be accommodated by the braneworld for a large region in parameter space $0 < Omega_l < 0.3$ at $1sigma$. The Hubble parameter can be as high as $H_0 < 78$ km/s/Mpc, and the effective equation of state at present can show phantom-like behaviour with $w_0 < -1.2$ at $1sigma$. We note a correlation between $H_0$ and $w_0$, with higher values of $H_0$ leading to a lower, and more phantom-like, value of $w_0$. Inclusion of CMB data provides tighter constraints $Omega_l < 0.1$. (Here $Omega_l$ encodes the ratio of the five and four dimensional Planck mass.) The Hubble parameter in this case is more tightly constrained to $H_0 < 71$ km/s/Mpc, and the effective equation of state to $w_0 < -1.1$. Interestingly, we find that the universe is allowed be closed or open, with $-0.5 < Omega_{kappa} < 0.5$, even on including the compressed CMB data. There appears to be some tension in the low and high $z$ BAO data which may either be resolved by future data, or act as a pointer to interesting new cosmology.
We derive a redshift drift formula for the spherically symmetric inhomogeneous pressure Stephani universes which are complementary to the spherically symmetric inhomogeneous density Lema^itre-Tolman-Bondi models. We show that there is a clear difference between redshift drift predictions for these two models as well as between the Stephani models and the standard $Lambda$CDM Friedmann models. The Stephani models have positive drift values at small redshift and behave qualitatively (but not quantitatively) as the $Lambda$CDM models at large redshift, while the drift for LTB models is always negative. This prediction may perhaps be tested in future telescopes such as European Extremely Large Telescope (EELT), Thirty Meter Telescope (TMT), Giant Magellan Telescope (GMT), and especially, in gravitational wave interferometers DECi-Hertz Interferometer Gravitational Wave Observatory and Big Bang Observer (DECIGO/BBO), which aim at low redshift.
Variation of the speed of light is quite a debated issue in cosmology with some benefits, but also with some controversial concerns. Many approaches to develop a consistent varying speed of light (VSL) theory have been developed recently. Although a lot of theoretical debate has sprout out about their feasibility and reliability, the most obvious and straightforward way to discriminate and check if such theories are really workable has been missed out or not fully employed. What is meant here is the comparison of these theories with observational data in a fully comprehensive way. In this paper we try to address this point i.e., by using the most updated cosmological probes, we test three different candidates for a VSL theory (Barrow & Magueijo, Avelino & Martins, and Moffat) signal. We consider many different ans{a}tze for both the functional form of $c(z)$ (which cannot be fixed by theoretical motivations) and for the dark energy dynamics, in order to have a clear global picture from which we extract the results. We compare these results using a reliable statistical tool such as the Bayesian Evidence. We find that the present cosmological data is perfectly compatible with any of these VSL scenarios, but in one case (Moffat model) we have a higher Bayesian Evidence ratio in favour of VSL than in the standard $c=$ constant $Lambda$CDM 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 $2sigma$ level) and is also falsifiable in the nearest future due to some peculiar issues which differentiate this model from the standard model. Finally, we have applied some priors which come from cosmology and, in particular, from information theory and gravitational thermodynamics.
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