Constraining Variationsin the Fine-Structure Constant, Quark Massesand the Strong Interaction

Abstract

We present evidence for variations in the fine-structure constant from Keck/HIRES spectra of 143 quasar absorption systems over the redshift range 0.2 < z abs < 4.2. This includes 15 new systems, mostly at high-z (z abs > 1.8). Our most robust estimate is a weighted mean ∆α/α = (−0.57 ± 0.11) × 10 −5 . We respond to recent criticisms of the many-multiplet method used to extract these constraints. The most important potential systematic error at low-z is the possibility of very different Mg heavy isotope abundances in the absorption clouds and laboratory: higher abundances of 25,26 Mg in the absorbers may explain the low-z results. Approximately equal mixes of 24 Mg and 25,26 Mg are required. Observations of Galactic stars generally show lower 25,26 Mg isotope fractions at the low metallicities typifying the absorbers. Higher values can be achieved with an enhanced population of intermediate mass stars at high redshift, a possibility at odds with observed absorption system element abundances. At present, all observational evidence is consistent with the varying-α results.Another promising method to search for variation of fundamental constants involves comparing different atomic clocks. Here we calculate the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of α and mq/ΛQCD from recent atomic clock experiments with hyperfine transitions in H, Rb, Cs, Hg + and an optical transition in Hg + .

Searching for spatial variations ofα2/μin the Milky Way

“…There was a claim for a variability in α at the 5σ confidence level: Δα/α = −5.7 ± 1.1 ppm (Murphy et al 2004) 1 , but this has not been confirmed in other measurements that led to the upper bound |Δα/α| < 2 ppm (Quast et al 2004;Levshakov et al 2005;Srianand et al 2008;Molaro et al 2008).…”

The UVES Large Program for testing fundamental physics – III. Constraints on the fine-structure constant from three telescopes

“…When King et al (2012) combined their VLT measurements with the Murphy et al (2004) Keck ones, they found internally consistent evidence for a dipolar variation in α across the sky. In order to have any confidence in this result, we must be assured that the α-dipole is the result of physics varying in different parts of the universe and not the result of systematic errors between observations and/or spectrographs.…”

“…Also, Murphy et al (2004) used HIRES to measure ∆α/α in all 3 of the absorbers towards J1551+1911 measured here. In all cases, the two sets of measurements agree within 1 σ (using the quadrature sum of uncertainties from both sets) for each absorption system.…”

“…The most surprising ∆α/α results come from a sample of 143 Keck/HIRES-observed absorption systems (Murphy et al 2003;Murphy et al 2004) and 154 VLT/UVES-observed absorption systems (Webb et al 2011;King et al 2012). When King et al (2012) combined their VLT measurements with the Murphy et al (2004) Keck ones, they found internally consistent evidence for a dipolar variation in α across the sky.…”

Reconstructing the evolution of dark energy with variations of fundamental parameters

“…Consequently, its dynamical evolution can result in extra interactions between standard particles, which are mediated by the field, and to a variation in the fundamental parameters. Curiously, it has been reported that observations of a number of quasar absorption lines suggest that the fine structure constant was smaller in the past, at redshifts in the range z = 1 − 3 (Murphy et al (2003), Murphy et al (2004), but see also Srianand et al (2007)). Could this indeed be the signature of a slowly evolving scalar field?…”