Revision of VLT/UVES constraints on a varying fine-structure constant

We critically review the current null results on a varying fine-structure constant, α, derived from Very Large Telescope (VLT)/Ultraviolet and Visual Echelle Spectrograph (UVES) quasar absorption spectra, focusing primarily on the many-multiplet analysis of 23 absorbers from which Chand et al. reported a weighted mean relative variation of  Δα/α= (?0.06 ± 0.06) × 10^?5  . Our analysis of the same reduced data , using the same fits to the absorption profiles , yields very different individual  Δα/α  values with uncertainties typically larger by a factor of ～3. We attribute the discrepancies to flawed parameter estimation techniques in the original analysis and demonstrate that the original  Δα/α  values were strongly biased towards zero. Were those flaws not present, the input data and spectra should have given a weighted mean of  Δα/α= (?0.44 ± 0.16) × 10^?5  . Although this new value does reflect the input spectra and fits (unchanged from the original work – only our analysis is different), we do not claim that it supports previous Keck/High Resolution Echelle Spectrograph (HIRES) evidence for a varying α: there remains significant scatter in the individual  Δα/α  values which may stem from the overly simplistic profile fits in the original work. Allowing for such additional, unknown random errors by increasing the uncertainties on  Δα/α  to match the scatter provides a more conservative weighted mean,  Δα/α= (?0.64 ± 0.36) × 10^?5  . We highlight similar problems in other current UVES constraints on varying α and argue that comparison with previous Keck/HIRES results is premature.