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New limits on the possible variation of physical constants

Authors:	MJ Drinkwater JK Webb JD Barrow VV Flambaum

Institution:	School of Physics, University of New South Wales, Sydney 2052, Australia;; Astronomy Centre, University of Sussex, Brighton BN1 9QH

Abstract:	Recent detections of high-redshift absorption by both atomic hydrogen and molecular gas in the radio spectra of quasars have provided a powerful tool for measuring possible temporal and spatial variations of physical 'constants' in the universe. We compare the frequency of high-redshift hydrogen 21-cm absorption with that of associated molecular absorption in two quasars to place new (1σ) upper limits on any variation in y≡g_pα² (where α is the fine-structure constant, and g_p is the proton g -factor of at redshifts z = 0.25 and 0.68. These quasars are separated by a comoving distance of 3000 Mpc ( H ₀= 75 km s^?1 Mpc^?1 and q ₀). We also derive limits on the time rates of change between the present epoch and z = 0.68. These limits are more than an order of magnitude smaller than previous results derived from high-redshift measurements.

Keywords:	ISM:atoms ISM:molecules quasars:absorption lines cosmology:observations