The fine-structure constant: a new observational limit on its cosmologicalvariation and some theoretical consequences

Endeavours of the unification of the four fundamental interactions have res ulted in a development of theories having cosmological solutions in which l ow-energy limits of fundamental physical constants vary with time. The vali dity of such theoretical models should be checked by comparison of the theo retical predictions with observational and experimental bounds on possible time-dependences of the fundamental constants. Based on high-resolution measurements of quasar spectra, we obtain the foll owing direct limits on the average rate of the cosmological time variation of the fine-structure constant alpha: \ (alpha) over dot/alpha \ < 1.9 x 10(-14) yr(-1) is the most likely limit, and \ (alpha) over dot/alpha \ < 3.1 x 10(-14) yr(-1) is the most conservative limit. Analogous estimates published previously, as well as other contemporary tes ts for possible variations of alpha (those based on the "Oklo phenomenon", on the primordial nucleosynthesis models, and others) are discussed and com pared with the present upper limit. We argue that the present result is the most conservative one.