Probing variations in the fundamental constants with quasar absorption lines

Details Probing variations in the fundamental constants with quasar absorption lines Probing variations in the fundamental constants with quasar absorption lines

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........3m&link_type=abstract

PhD thesis, University of New South Wales

Mathematics

Logic

14

Quasar, Absorption, Fundamental, Constants, Fine-Structure Constant

Scientific paper

Precision cosmology challenges many aspects of fundamental physics. In particular, quasar absorption lines test the assumed constancy of fundamental constants over cosmological time-scales and distances. Until recently, the most reliable technique was the alkali doublet (AD) method where the measured doublet separation probes variations in the fine-structure constant, alpha=e^2/hbar/c. However, the recently introduced many-multiplet (MM) method provides several advantages, including a demonstrated 10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with 0.2 < z_abs < 3.7. We find 5.6-sigma statistical evidence for a smaller alpha in the absorption clouds: da/a=(-0.574 +/- 0.102)x10^{-5}. All three samples separately yield consistent, significant da/a. The data marginally prefer constant da/dt rather than constant da/a. The two-point correlation function for alpha and the angular distribution of da/a give no evidence for spatial variations. We also analyse 21 Keck/HIRES SiIV doublets, obtaining a 3-fold relative precision gain over previous AD studies: da/a=(-0.5 +/- 1.3)x10^{-5} for 2.0 < z_abs < 3.1.
Our statistical evidence for varying alpha requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on da/a. Cosmological variation in Mg isotopic abundances may affect da/a at z_abs < 1.8. Galactic observations and theory suggest diminished 25,26Mg abundances in the low metallicity quasar absorbers. Removing 25,26Mg isotopes yields more negative da/a values. Overall, known systematic errors can not explain our results.
We also constrain variations in y=alpha^2g_p, comparing HI 21-cm and millimetre-wave molecular absorption in 2 systems. Fitting both the HI and molecular lines yields the tightest, most reliable current constraints: dy/y=(-0.20 +/- 0.44)x10^{-5} and (-0.16 +/- 0.54)x10^{-5} at z_abs=0.2467 and 0.6847 respectively. Possible line-of-sight velocity differences between the HI and molecular absorbing regions dominate these 1-sigma errors. A larger sample of mm/HI comparisons is required to reliably quantify this uncertainty and provide a potentially crucial check on the MM result.

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