Relativistic effects in NiII and the search for variation of the fine-structure constant - art. no. 042509

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical "constants" in the Universe. De tection of high redshift absorption systems intersecting the sight lines to ward distant quasars provides a powerful tool for measuring these variation s. In the present paper we demonstrate that high sensitivity to variation o f the fine-structure constant a can be obtained by comparing cosmic and lab oratory spectra of the Ni II ion. Relativistic effects in Ni II reveal many interesting features. The Ni II spectrum exhibits avoided level crossings under variation of a and the intervals between the levels have strong nonli near dependencies on relativistic corrections. The values of the transition frequency shifts, due to the change of alpha, vary significantly from stat e to state including changes of sign. This enhances the sensitivity to the variation of alpha and reduces possible systematic errors. Calculations of the a dependence of the nickel ion spectral lines that an detectable in qua sar absorption spectra have been performed using a relativistic configurati on interaction method.