An order of magnitude sensitivity gain is described for using quasar spectra to investigate possible time or space variation in the fine structure constant a. Applied to a sample of 30 absorption systems, spanning redshifts 0.5 , z , 1.6, we derive limits on variations in a over a wide range of epochs. For the whole sample, Da͞a ͑21.1 6 0.4͒ 3 10 25 . This deviation is dominated by measurements at z . 1, where Da͞a ͑21.9 6 0.5͒ 3 10 25 . For z , 1, Da͞a ͑20.2 6 0.4͒ 3 10 25 . While this is consistent with a time-varying a, further work is required to explore possible systematic errors in the data, although careful searches have so far revealed none. [S0031-9007(98)08267-2] PACS numbers: 06.20. Jr, 95.30.Dr, 95.30.Sf, 98.80.Es There are several theoretical motivations to search for space-time variations in the fine structure "constant," a. Theories which attempt to unify gravity and other fundamental forces may require the existence of additional compact space dimensions. Any cosmological evolution in the mean scale factor of these additional dimensions will manifest itself as a time variation of our bare three-dimensional coupling constants [1]. Alternatively, theories have been considered which introduce new scalar fields whose couplings with the Maxwell scalar F ab F ab allow a time-varying a [2]. The measurement of any variation in a would clearly have profound implications for our understanding of fundamental physics.Spectroscopic observations of gas clouds seen in absorption against background quasars can be used to search for time variation of a. Analyses involving optical spectroscopy of quasar absorbers have concentrated on the relativistic fine-structure splitting of alkali-type doublets; the separation between lines in one multiplet is proportional to a 2 , so small variations in the separation are directly proportional to a, to a good approximation.While the simplicity of that method is appealing, the relativistic effect causing the fine splitting is small, restricting the potential accuracy. We demonstrate below how a substantial sensitivity gain is achieved by comparing the wavelengths of lines from different species, and develop a new procedure, simultaneously analyzing the Mg II 2796͞2803 doublet and up to five Fe II transitions (Fe II 2344, 2374, 2383, 2587, 2600 Å) from three different multiplets. These particular transitions are chosen for the following reasons: (i) They are commonly seen in quasar absorption systems; (ii) they fall into and span a suitable rest-wavelength range; (iii) an excellent database was available [3]; (iv) extremely precise laboratory wavelengths have been measured; and (v) the large Fe and Mg nuclear charge difference yields a considerable sensitivity gain.We describe the details of the theoretical developments in a separate paper [4], here summarizing the main points. The energy equation for a transition from the ground state within a particular multiplet, observed at some redshift z, is given bywhere Z is the nuclear charge, L and S are the electron total orbital ...

We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant, α, at high redshift. New Very Large Telescope (VLT) data, probing a different direction in the universe, shows an inverse evolution; α increases at high redshift. Although the pattern could be due to as yet undetected systematic effects, with the systematics as presently understood the combined dataset fits a spatial dipole, significant at the 4.2σ level, in the direction right ascension 17.5±0.9 hours, declination −58±9 degrees. The independent VLT and Keck samples give consistent dipole directions and amplitudes, as do high and low redshift samples. A search for systematics, using observations duplicated at both telescopes, reveals none so far which emulate this result.PACS numbers: 06.20. Jr, 95.30.Dr, 95.30.Sf, 98.62.Ra, 98.80.Es, 98.80.Jk Quasar spectroscopy as a test of fundamental physics.-The vast light-travel times to distant quasars allow us to probe physics at high redshift. The relative wavenumbers, ω z , of atomic transitions detected at redshift z = λ obs /λ lab − 1, can be compared with laboratory values, ω 0 , via the relationshipwhere the coefficient Q measures the sensitivity of a given transition to a change in α. The variation in both magnitude and sign of Q for different transitions is a significant advantage of the Many Multiplet method [1, 2], helping to combat potential systematics.The first application of this method, 30 measurements of ∆α/α = (α z − α 0 ) /α 0 , indicated a smaller α at high redshift at the 3σ significance level. By 2004 we had made 143 measurements of α covering a wide redshift range, using further data from the Keck telescope obtained by 3 separate groups, supporting our earlier findings, that towards that general direction in the universe at least, α may have been smaller at high redshift, at the 5σ level [3][4][5]. The constant factor at that point was (undesirably) the telescope and spectrograph.New data from the VLT.-We have now analysed a large dataset from a different observatory, the VLT. Full details and searches for systematic errors will be given elsewhere [6,7]. Here we summarize the evidence for spatial variation in α emerging from the combined Keck+VLT samples. Quasar spectra, obtained from the ESO Science Archive, were selected, prioritising primarily by expected signal to noise but with some preference given to higher redshift objects and to objects giving more extensive sky coverage. The ESO midas pipeline was used for the first data reduction step, including wavelength calibration, although enhancements were made to derive a more robust and accurate wavelength solution from an improved selection of thorium-argon calibration lamp emission lines [8]. Echelle spectral orders from several exposures of a given quasar were combined using uves popler [9]. A total of 60 quasar spectra from the VLT have been used for the present work, yielding 153 absorption systems. Absorption systems were identified via a careful visual search of each spectrum, us...

High-precision measurements of violations of fundamental symmetries in atoms are a very effective means of testing the standard model of elementary particles and searching for new physics beyond it. Such studies complement measurements at high energies. We review the recent progress in atomic parity nonconservation and atomic electric dipole moments (time reversal symmetry violation), with a particular focus on the atomic theory required to interpret the measurements.

We describe the results of a search for time variability of the fine structure constant alpha using absorption systems in the spectra of distant quasars. Three large optical data sets and two 21 cm and mm absorption systems provide four independent samples, spanning approximately 23% to 87% of the age of the universe. Each sample yields a smaller alpha in the past and the optical sample shows a 4 sigma deviation: Delta alpha/alpha = -0.72+/-0.18 x 10(-5) over the redshift range 0.5

We have previously presented evidence for a varying fine‐structure constant, α, in two independent samples of Keck/HIRES quasi‐stellar object (QSO) absorption spectra. Here we present a detailed many‐multiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also re‐analyse the previous samples, providing a total of 128 absorption systems over the redshift range 0.2 < zabs < 3.7. The results, with raw statistical errors, indicate a smaller weighted mean α in the absorption clouds: Δα/α= (−0.574 ± 0.102) × 10−5. All three samples separately yield consistent and significant values of Δα/α. The analyses of low‐z (i.e. zabs < 1.8) and high‐z systems rely on different ions and transitions with very different dependences on α, yet they also give consistent results. We identify an additional source of random error in 22 high‐z systems characterized by transitions with a large dynamic range in apparent optical depth. Increasing the statistical errors on Δα/α for these systems gives our fiducial result, a weighted mean Δα/α= (−0.543 ± 0.116) × 10−5, representing 4.7σ evidence for a varying α. Assuming that Δα/α= 0 at zabs= 0, the data marginally prefer a linear increase in α with time rather than a constant offset from the laboratory value: . The two‐point correlation function for α is consistent with zero over 0.2–13 Gpc comoving scales and the angular distribution of Δα/α shows no significant dipolar anisotropy. We therefore have no evidence for spatial variations in Δα/α. We extend our previous searches for possible systematic errors, giving detailed analyses of potential kinematic effects, line blending, wavelength miscalibration, spectrograph temperature variations, atmospheric dispersion and isotopic/hyperfine structure effects. The latter two are potentially the most significant. However, overall, known systematic errors do not explain the results. Future many‐multiplet analyses of independent QSO spectra from different telescopes and spectrographs will provide a now crucial check on our Keck/HIRES results.

An ab initio method for high accuracy calculations for atoms with more than one valence electron is described. The effective Hamiltonian for the valence electrons is formed using many-body perturbation theory for the interaction of the valence electrons with the core. The configuration-interaction method is then used to find the energy levels of the atom. An application of this to thallium shows that the method gives an accuracy of about 0.5% for the ionization potential and a few tenths of a percent for the first few energy intervals.

Quasar absorption lines provide a precise test of whether the fine‐structure constant, α, is the same in different places and through cosmological time. We present a new analysis of a large sample of quasar absorption‐line spectra obtained using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) in Chile. We apply the many‐multiplet method to derive values of Δα/α≡ (αz−α0)/α0 from 154 absorbers, and combine these values with 141 values from previous observations at the Keck Observatory in Hawaii. In the VLT sample, we find evidence that α increases with increasing cosmological distance from Earth. However, as previously shown, the Keck sample provided evidence for a smaller α in the distant absorption clouds. Upon combining the samples, an apparent variation of α across the sky emerges which is well represented by an angular dipole model pointing in the direction RA = 17.3 ± 1.0 h and Dec. =−61°± 10°, with amplitude . The dipole model is required at the 4.1σ statistical significance level over a simple monopole model where α is the same across the sky (but possibly different from the current laboratory value). The data sets reveal remarkable consistencies: (i) the directions of dipoles fitted to the VLT and Keck samples separately agree; (ii) the directions of dipoles fitted to z < 1.6 and z > 1.6 cuts of the combined VLT+Keck samples agree; and (iii) in the equatorial region of the dipole, where both the Keck and VLT samples contribute a significant number of absorbers, there is no evidence for inconsistency between Keck and VLT. The amplitude of the dipole is clearly larger at higher redshift. Assuming a dipole‐only (i.e. no‐monopole) model whose amplitude grows proportionally with ‘lookback‐time distance’ (r=ct, where t is the lookback time), the amplitude is (1.1 ± 0.2) × 10−6 GLyr−1 and the model is significant at the 4.2σ confidence level over the null model (Δα/α≡ 0). We apply robustness checks and demonstrate that the dipole effect does not originate from a small subset of the absorbers or spectra. We present an analysis of systematic effects, and are unable to identify any single systematic effect which can emulate the observed variation in α. To the best of our knowledge, this result is not in conflict with any other observational or experimental result.

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical "constants" in the Universe. Detection of high-redshift absorption systems intersecting the sight lines towards distant quasars provide a powerful tool for measuring these variations. We have previously demonstrated that high sensitivity to the variation of the fine structure constant α can be obtained by comparing spectra of heavy and light atoms (or molecules). Here we describe new calculations for a range of atoms and ions, most of which are commonly detected in quasar spectra: Fe II, Mg II, Mg I, C II, C IV, N V, O I, Al III, Si II, Si IV, Ca I, Ca II, Cr II, Mn II, Zn II, Ge II (see the results in Table 3). The combination of Fe II and Mg II, for which accurate laboratory frequencies exist, have already been used to constrain α variations. To use other atoms and ions, accurate laboratory values of frequencies of the strong E1-transitions from the ground states are required. We wish to draw the attention of atomic experimentalists to this important problem.We also discuss a mechanism which can lead to a greatly enhanced sensitivity for placing constraints on variation on fundamental constants. Calculations have been performed for Hg II, Yb II, Ca I and Sr II where there are optical transitions with the very small natural widths, and for hyperfine transition in Cs I and Hg II. 06.20.Jr , 31.30.Jv , 95.30.Dr