An Observational Determination of the Proton to Electron Mass Ratio in the Early Universe

In an effort to resolve the discrepancy between two measurements of the fundamental constant Delta *m, the proton to electron mass ratio, at early times in the universe we reanalyze the same data used in the earlier studies. Our analysis of the molecular hydrogen absorption lines in archival Very La...

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Bibliographic Details
Published in:The Astrophysical journal 2009-10, Vol.703 (2), p.1648-1662
Main Authors: Thompson, Rodger I, Bechtold, Jill, Black, John H, Eisenstein, Daniel, Fan, Xiaohui, Kennicutt, Robert C, Martins, Carlos, Prochaska, J. Xavier, Shirley, Yancey L
Format: Article
Language:English
Subjects:
ABSORPTION
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BARYONS
CALIBRATION
Earth, ocean, space
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
Exact sciences and technology
FERMIONS
FUNDAMENTAL CONSTANTS
HADRONS
LEPTONS
M-THEORY
MATTER
MEASURING INSTRUMENTS
NONLUMINOUS MATTER
NUCLEONS
PROTONS
RADIATIONS
RED SHIFT
SCALAR FIELDS
SORPTION
SPECTROMETERS
STRING THEORY
SUPERSYMMETRY
SYMMETRY
TELESCOPES
ULTRAVIOLET RADIATION
UNIVERSE
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Summary:In an effort to resolve the discrepancy between two measurements of the fundamental constant Delta *m, the proton to electron mass ratio, at early times in the universe we reanalyze the same data used in the earlier studies. Our analysis of the molecular hydrogen absorption lines in archival Very Large Telescope/Ultraviolet and Visible Echelle Spectrometer (UVES) spectra of the damped Lyman alpha systems in the quasi-stellar objects Q0347-383 and Q0405-443 yields a combined measurement of a Delta *D Delta *m/ Delta *m value of (-7 +/- 8) X 10-6, consistent with no change in the value of Delta *m over a time span of 11.5 Gyr. Here, we define Delta *D Delta *m as ( Delta *m z - Delta *m0) where Delta *m z is the value of Delta *m at a redshift of z and Delta *m0 is the present-day value. Our null result is consistent with the recent measurements of King et al., Delta *D Delta *m/ Delta *m = (2.6 +/- 3.0) X 10-6, and inconsistent with the positive detection of a change in Delta *m by Reinhold et al. Both of the previous studies and this study are based on the same data but with differing analysis methods. Improvements in the wavelength calibration over the UVES pipeline calibration is a key element in both of the null results. This leads to the conclusion that the fundamental constant Delta *m is unchanged to an accuracy of 10-5 over the last 80% of the age of the universe, well into the matter dominated epoch. This limit provides constraints on models of dark energy that invoke rolling scalar fields and also limits the parameter space of supersymmetric or string theory models of physics. New instruments, both planned and under construction, will provide opportunities to greatly improve the accuracy of these measurements.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/703/2/1648