Probing Variations In The Fundamental Constants With Quasar Absorption Lines

Michael T. Murphy, John K. Webb, Victor V. Flambaum
2003 Zenodo  
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, \(\alpha \equiv e^2/\hbar c\). However, the recently introduced many-multiplet (MM) method provides several advantages,
more » ... a demonstrated ≈10-fold precision gain. This thesis presents detailed MM analyses of 3 independent Keck/HIRES samples containing 128 absorption systems with \(0.2 < z_{\rm abs} < 3.7\). We find \(5.6\sigma\) statistical evidence for a smaller α in the absorption clouds: \(\Delta\alpha/\alpha = (-0.574 \pm 0.102) \times 10^{-5}\). All three samples separately yield consistent, significant \(\Delta\alpha/\alpha\). The data marginally prefer constant \(d\alpha/dt\) rather than constant \(\Delta\alpha/\alpha\). The two-point correlation function for α and the angular distribution of \(\Delta\alpha/\alpha\) give no evidence for spatial variations. We also analyse 21 Keck/HIRES Si iv doublets, obtaining a 3-fold relative precision gain over previous AD studies: \(\Delta\alpha/\alpha = (0.5 \pm 1.3) \times 10^{-5}\) for \(2.0 < z_{\rm abs} < 3.1\). Our statistical evidence for varying α requires careful consideration of systematic errors. Modelling demonstrates that atmospheric dispersion is potentially important. However, the quasar spectra suggest a negligible effect on \(\Delta\alpha/\alpha\). Cosmological variation in Mg isotopic abundances may affect \(\Delta\alpha/\alpha\) at \(z_{\rm abs} < 1.8\). Galactic observations and theory suggest diminished 25,26Mg abundances in the low metallicity quasar absorbers. Removing 25,26Mg isotopes yields more negative \(\Delta\alpha/\alpha\) values. Overall, known systematic errors can not explain our results. We also constrain variations in \(y = \a [...]
doi:10.5281/zenodo.57184 fatcat:kbk4nacsdbapje74odbtptrp6a