Ultralight bosons such as axion-like particles are viable candidates for dark matter. They can form stable, macroscopic field configurations in the form of topological defects that could concentrate the dark matter density into many distinct, compact spatial regions that are small compared with the Galaxy but much larger than the Earth. Here we report the results of the search for transient signals from the domain walls of axion-like particles by using the global network of optical magnetometers for exotic (GNOME) physics searches. We search the data, consisting of correlated measurements from optical atomic magnetometers located in laboratories all over the world, for patterns of signals propagating through the network consistent with domain walls. The analysis of these data from a continuous month-long operation of GNOME finds no statistically significant signals, thus placing experimental constraints on such dark matter scenarios.

Observations of the redshift z = 7.085 quasar J1120+0641 are used to search for variations of the fine structure constant, α, over the redshift range 5.5 to 7.1. Observations at z = 7.1 probe the physics of the universe at only 0.8 billion years old. These are the most distant direct measurements of α to date and the first measurements using a near-IR spectrograph. A new AI analysis method is employed. Four measurements from the x-shooter spectrograph on the Very Large Telescope (VLT) constrain changes in a relative to the terrestrial value (α₀). The weighted mean electromagnetic force in this location in the universe deviates from the terrestrial value by Δα/α = (α_z − α₀)/α₀ = (−2.18 ± 7.27) × 10⁻⁵, consistent with no temporal change. Combining these measurements with existing data, we find a spatial variation is preferred over a no-variation model at the 3.9σ level.

The primordial deuterium abundance probes fundamental physics during the Big Bang Nucleosynthesis and can be used to infer cosmological parameters. Observationally, the abundance can be measured using absorbing clouds along the lines of sight to distant quasars. Observations of the quasar PKS1937–101 contain two absorbers for which the deuterium abundance has previously been determined. Here we focus on the higher redshift one at z_abs = 3.572. We present new observations with significantly increased signal-to-noise ratio which enable a far more precise and robust measurement of the deuterium to hydrogen column density ratio, resulting in D i/H i = 2.62 ± 0.05 × 10⁻⁵. This particular measurement is of interest because it is among the most precise assessments to date and it has been derived from the second lowest column-density absorber [N(H i) = 17.9 cm⁻²] that has so-far been utilised for deuterium abundance measurements. The majority of existing high-precision measurements were obtained from considerably higher column density systems [i.e. N(H i) > 19.4 cm⁻²]. This bodes well for future observations as low column density systems are more common.

The primordial deuterium abundance is an important tracer of the fundamental physics taking place during big bang nucleosynthesis. It can be determined from absorption features along the line of sight to distant quasars. The quasar PKS 1937−1009 contains two absorptions systems that have been used to measure the primordial deuterium abundance, the lower redshift one being at z_abs = 3.256. New observations of this absorber are of a substantially higher signal-to-noise ratio and thus permit a significantly more robust estimate of the primordial deuterium abundance, leading to a D i/H i ratio of 2.45 ± 0.28 × 10⁻⁵. Whilst the precision of the new measurement presented here is below that obtained from the recent cosmological parameter measurements by the Planck Surveyor, our analysis illustrates how a statistical sample obtained using similarly high spectral signal-to-noise ratio can make deuterium a competitive and complementary cosmological parameter estimator and provide an explanation for the scatter seen between some existing deuterium measurements.

The spectrum of the z_em = 2.63 quasar Q1009+2956 has been observed extensively on the Keck telescope. The Lyman limit absorption system z_abs = 2.504 was previously used to measure D/H by Burles & Tytler using a spectrum with signal to noise (S/N) approximately 60 per pixel in the continuum near Ly α at z_abs = 2.504. The larger data set now available combines to form an exceptionally high S/N spectrum, around 147 per pixel. Several heavy element absorption lines are detected in this Lyman limit system, providing strong constraints on the kinematic structure. We explore a suite of absorption system models and find that the deuterium feature is likely to be contaminated by weak interloping Ly α absorption from a low column density Hi cloud, reducing the expected D/H precision. We find D/H |$=2.48^{+0.41}_{-0.35} \times 10^{-5}$| for this system. Combining this new measurement with others from the literature and applying the method of Least Trimmed Squares to a statistical sample of 15 D/H measurements results in a ‘reliable’ sample of 13 values. This sample yields a primordial deuterium abundance of (D/H)_p = (2.545 ± 0.025) × 10⁻⁵. The corresponding mean baryonic density of the Universe is Ω_bh² = 0.02174 ± 0.00025. The quasar absorption data are of the same precision as, and marginally inconsistent with, the 2015 CMB Planck (TT+lowP+lensing) measurement, Ω_bh² = 0.02226 ± 0.00023. Further quasar and more precise nuclear data are required to establish whether this is a random fluctuation.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics