Extra Dimensions and Varying Alpha

We use recent astrophysical and local tests of the stability of the fine-structure constant, $\alpha$, to constrain a particular phenomenological but physically motivated class of models in which the dark energy equation of state can undergo a rapid transition at low redshifts, perhaps associated with the onset of the acceleration phase. We set constraints on the phenomenological parameters describing such possible transitions, in particular improving previous constraints (wh...

Any time variation in the fine-structure constant alters the ionization history of the universe and therefore changes the pattern of cosmic microwave background fluctuations. We calculate the changes in the spectrum of these fluctuations as a function of the change in the fine-structure constant, and we find that these changes are dominated by the change in the redshift of recombination due to the shift in the binding energy of hydrogen. We estimate the accuracy with which th...

Time variation of fundamental constants would not be surprising in the framework of theories involving extra dimensions. The variation of any one constant is likely to be correlated with variations of others in a pattern that is diagnostic of the underlying physics.

We describe the results of a search for time variability of the fine structure constant, alpha, using absorption systems in the spectra of distant quasars. Three large optical datasets and two 21cm/mm absorption systems provide four independent samples, spanning 23% to 87% of the age of the universe. Each sample yields a smaller alpha in the past and the optical sample shows a 4-sigma deviation: da/a = -0.72 +/- 0.18 x 10^{-5} over the redshift range 0.5 < z < 3.5. We find no...

Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant $\alpha$, are a powerful probe of new physics. Recently these measurements, combined with local atomic clock tests and Type Ia supernova and Hubble parameter data, were used to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, $\zeta$, to the electromagne...

Using the BSBM varying-alpha theory, with dark matter dominated by magnetic energy, and the spherical collapse model for cosmological structure formation, we have studied the effects of the dark-energy equation of state and the coupling of alpha to the matter fields on the space and time evolution of alpha. We have compared its evolution inside virialised overdensities with that in the cosmological background, using the standard ($% \Lambda =0$) $CDM$ model of structure forma...

We determine the behaviour of a time-varying fine structure 'constant' $\alpha (t)$ during the early and late phases of universes dominated by the kinetic energy of changing $\alpha (t)$, radiation, dust, curvature, and lambda, respectively. We show that after leaving an initial vacuum-dominated phase during which $\alpha$ increases, $\alpha$ remains constant in universes like our own during the radiation era, and then increases slowly, proportional to a logarithm of cosmic t...

The constraints on the time variation of the fine structure constant at recombination epoch relative to its present value, $\Delta\alpha/\alpha \equiv (\alpha_{\mathrm{rec}} - \alpha_{\mathrm{now}})/\alpha_{\mathrm{now}}$, are obtained from the analysis of the 5-year WMAP cosmic microwave background data. As a result of Markov-Chain Monte-Carlo analysis, it is found that, contrary to the analysis based on the previous WMAP data, the mean value of $\Delta\alpha/\alpha=-0.0009$...

There are indications from the study of quasar absorption spectra that the fine structure constant $\alpha$ may have been measurably smaller for redshifts $z>2.$ Analyses of other data ($^{149}$Sm fission rate for the Oklo natural reactor, variation of $^{187}$Re $\beta$-decay rate in meteorite studies, atomic clock measurements) which probe variations of $\alpha$ in the more recent past imply much smaller deviations from its present value. In this work we tie the variation o...

We study the $\Lambda(\alpha)$CDM models with $\Lambda(\alpha)$ being a function of the time-varying fine structure constant $\alpha$. We give a close look at the constraints on two specific $\Lambda(\alpha)$CDM models with one and two model parameters, respectively, based on the cosmological observational measurements along with 313 data points for the time-varying $\alpha$. We find that the model parameters are constrained to be around $10^{-4}$, which are similar to the re...