DIFFERENTIAL MEASUREMENTS OF THE FINE-STRUCTURE CONSTANT FROM QUASAR SPECTRA - A TEST OF KALUZA-KLEIN COSMOLOGIES

Kaluza-Klein theories, which predict variability of the fine-structure constant alpha = e2/hcBAR, are tested using new high-resolution observations of resonance doublets of Na-like ions observed in QSO absorption spectra at different redshifts. Previous results on the cosmic time variability of alpha have been revised. The statistical correlations between errors in experimentally measured data are considered, and the generalized probability density function of the alpha(z)/alpha ratio (alpha(z) is the value of alpha at redshift z) is derived. The shape of this function is shown to be asymmetric. As a result, all estimates of sample means [alpha(z)/alpha] obtained previously appear to be biased. The upper limit, \DELTAalpha/alpha\ less-than-or-equal-to 0.5 per cent at z approximately 0.4, is derived on the basis of two isolated Mg II lambdalambda2796, 2804 doublets, which show symmetrical profiles at high resolution. This limit restricts any changes in the size of the extra dimensions in Kaluza-Klein models to about 0.3 per cent since z congruent-to 0.4. It is shown that new observations of the fine-structure splitting in the Na-23 I and Al-27 III resonance doublets, with improved resolution and sensitivity, may yield higher accuracy (approximately 0.01 per cent) in differential measurements of alpha from the quasar absorption-line spectra.