title: Methods for constraining fine structure constant evolution with OH microwave transitions.
abstract: We investigate the constraints that OH microwave transitions in megamasers and molecular absorbers at cosmological distances may place on the evolution of the fine structure constant alpha=e(2)/ variant Planck's over 2pi c. The centimeter OH transitions are a combination of hyperfine splitting and lambda doubling that can constrain the cosmic evolution of alpha from a single species, avoiding systematic errors in alpha measurements from multiple species which may have relative velocity offsets. The most promising method compares the 18 and 6 cm OH lines, includes a calibration of systematic errors, and offers multiple determinations of alpha in a single object. Comparisons of OH lines to the HI 21 cm line and CO rotational transitions also show promise.
authors.affiliation: Carnegie Observatories, 813 Santa Barbara Street, Pasadena, California 91101, USA.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Darling