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Variation in the fine structure constant?: Recent results and the future

Variation in the fine structure constant?: Recent results and the future. Michael Murphy, UNSW. Project leader: John Webb, UNSW. Collaborators: Victor Flambaum, UNSW Vladimir Dzuba, UNSW Chris Churchill, Penn. State Jason Prochaska, OCIW Arthur Wolfe, UCSD

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Variation in the fine structure constant?: Recent results and the future

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  1. Variation in the fine structure constant?: Recent results and the future Michael Murphy, UNSW Project leader: John Webb, UNSW Collaborators: Victor Flambaum, UNSW Vladimir Dzuba, UNSW Chris Churchill, Penn. State Jason Prochaska, OCIW Arthur Wolfe, UCSD John Barrow, Cambridge Francois Combes, Obs. Paris Tommy Wiklind, OSO Wallace Sargent, CalTech Rob Simcoe, CalTech Special thanks to: Anne Thorne, IC Juliet Pickering, IC Richard Learner, IC Ulf Griesmann, NIST Rainer Kling, NIST Sveneric Johansson, Lund U. Ulf Litzén, Lund U. for dedicated laboratory measurements

  2. Variation in the fine structure constant?: Recent results and the future Outline: • Motivations for varying constants, particularly the fine structure constant a=e2/hc • Previous experimental limits on a variability • Quasar absorption systems and the new, many-multiplet method • Our recent results • Potential systematic effects • A sneak peek at some new preliminary results • Conclusions? University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  3. Variation in the fine structure constant?: Recent results and the future Motivations for varying constants • 1937: Dirac and Milne suggested varying G. • String theory: extra spatial dimensions compactified on tiny scales. • Our (3+1)-dimensional constants related to scale sizes of extra dimensions. • M-theory: gravity acts in all 11 dimensions but other forces (EM, strong, weak) act only in 4-dimensions. • Expect variations in G on small (~0.1mm) scales. • But no variations in coupling constants like a=e2/hc. • a is most accessible to experimental tests of its constancy. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  4. Variation in the fine structure constant?: Recent results and the future Motivations for varying constants: • Varying-speed-of-light (VSL) theories can solve the “cosmological problems”. • Bekenstein (1982) first formulated a varying e theory in which variations in e are driven by spacetime variations of a scalar field. • Sandvik, Barrow & Magueijo (2001) have recast Bekenstein’s theory in terms of a varying c. • Their theory predicts cosmological variations in a. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  5. Variation in the fine structure constant?: Recent results and the future Previous limits on Da/a: Lab. constraints • Different atomic clocks tick with different dependencies on a. • The relativistic corrections are of order (Za)2. • Comparison of Hydrogen maser and Hg I clocks yielded Da/a1.4×10-14 over 140 days (Prestage et al. 1995). University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  6. Variation in the fine structure constant?: Recent results and the future Previous limits on Da/a: The Oklo bound • 1972: Discovery of 235U depletion in a mine in Gabon, Africa (stolen by high-tech terrorists?!). • Explanation: a natural fission reactor operated over 1.8 billion years ago! Zone 15: Natural Uranium Oxide (“yellowcake”) University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  7. Variation in the fine structure constant?: Recent results and the future Previous limits on Da/a: The Oklo bound • Heavy nuclei have very sharp resonances in their neutron absorption cross-section. • Thus, abundances of decay products of 235U fission give constraints on variation in the nuclear energies and thus a constraint on Da/a. • 1976:Shylakter first analyzed Samarium abundances from Oklo to constrain Da/a. • 1996: Damour & Dyson re-analyzed the same data to obtain a stronger constraint: Da/a<1×10-7. • 2000: Fujii et al. find Da/a=(-0.04±0.15)×10-7 from new data. BUTIt is still not clear if these results are meaningful at all! There is much debate over the theory used to obtain Da/a from the Samarium abundances. The upper limits on Da/a might have to be weakened by a factor of more than 100! This is work in progress. Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

  8. Variation in the fine structure constant?: Recent results and the future Constraints from QSO absorption lines: Quasar To Earth Lyaem Lya Lyman limit SiII CII SiIV SiII CIV Lyb Lybem NVem Lya forest CIVem SiIVem University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  9. Variation in the fine structure constant?: Recent results and the future Constraints from QSO absorption lines: • To resolve individual velocity components in a QSO spectrum we need high resolution (FWHM~7 kms-1). • Large wavelength coverage  echelle spectrograph. • High SNR  large aperture telescope. Clear blue sky ! W. M. Keck telescopes at 14,000 ft Muana Kea (Big Mountain) in Hawaii: cold, high and dry. 10-m (!!!) segmented primary mirror University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  10. Variation in the fine structure constant?: Recent results and the future Echellogram Constraints from QSO absorption lines: One dimensional spectrum Fine absorption lines from intervening gas Two dimensional spectrum l University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  11. Variation in the fine structure constant?: Recent results and the future Constraints from QSO absorption lines: • A Keck/HIRES doublet Quasar Q1759+75 H emission Over 60 000 data points! H absorption C IV doublet Metal absorption C IV 1550Å C IV 1548Å University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  12. Variation in the fine structure constant?: Recent results and the future The alkali doublet (AD) method • The wavelength spacing between components of the same doublet of transitions in an alkali-like ion (e.g. CIV, SiIV and MgII) is roughly proportional to a for small Da/a. • 1976: Wolfe, Brown & Roberts first applied the AD method to intervening MgII absorption lines. • 2000: Varshalovich et al. recently obtained Da/a=(-4.6 ± 4.3 ± 1.4)×10-5 using the AD method with 16 Si IV absorption systems (average redshift=zavg=2.6). • 2001: We have used improved lab wavelengths and new data from Keck to find Da/a=(-0.5 ±1.3)×10-5 (zavg=2.8). University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  13. Variation in the fine structure constant?: Recent results and the future The alkali doublet (AD) method • The AD method is simple … but inefficient. • The common S ground state in ADs has maximal relativistic corrections! University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  14. Variation in the fine structure constant?: Recent results and the future The many multiplet (MM) method • Relativistic corrections for many-electron atoms: • Compare light (Z~10) and heavy (Z~50) ions OR • S  P and D  P transitions in heavy ions. • More formally, we write the transition frequency as wz=w0+q1x for x=(az/a0)2 –1. • We must calculate q1 and measure w0. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  15. Variation in the fine structure constant?: Recent results and the future Advantages of the MM method: • ALL relativistic corrections (i.e. even the ground state)  order of magnitude gain in precision. • All transitions appearing in a QSO absorption system may be used  statistical gain. • Many transitions  reliable determination of the velocity structure. • Positive and negative q1 reduce systematic effects. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  16. Variation in the fine structure constant?: Recent results and the future Low-redshift data (MgII/FeII systems): University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  17. Variation in the fine structure constant?: Recent results and the future High-redshift data (damped Lya systems): University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  18. Variation in the fine structure constant?: Recent results and the future Results: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  19. Variation in the fine structure constant?: Recent results and the future Potential systematic effects: • Laboratory wavelength errors • Wavelength miscalibration • Heliocentric velocity variation • Temperature/Pressure changes during observations • Line blending • Differential isotopic saturation • Hyperfine structure effects • Instrumental profile variations • … and of course, Magnetic fields • Atmospheric refraction effects • Isotopic ratio evolution University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  20. Variation in the fine structure constant?: Recent results and the future Wavelength calibration: • Spectra calibrated with ThAr exposures ThAr lines Quasar spectrum • Treat ThAr lines like QSO absorption lines: QSO line: wz=w0QSO+q1x ThAr line: wz=w0ThAr+q1x University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  21. Variation in the fine structure constant?: Recent results and the future ThAr calibration results: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  22. Variation in the fine structure constant?: Recent results and the future Atmospheric refraction effects: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  23. Variation in the fine structure constant?: Recent results and the future Atmospheric refraction corrected results: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  24. Variation in the fine structure constant?: Recent results and the future Isotopic ratio evolution: • Isotopic ratios are predicted and measured to vary strongly with metallicity. • For Mg and Si, the weaker isotopes get weaker with decreasing [Fe/H]. • Our absorption systems have 0.01< [Fe/H] < 1.0. • Test: remove Mg and Si isotopes from our analysis. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  25. Variation in the fine structure constant?: Recent results and the future Zero isotopic ratio results: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  26. Variation in the fine structure constant?: Recent results and the future Other consistency checks: • Line removal: remove each transition and fit for Da/a again. Compare the Da/a’s before and after line removal. We have done this for all species and see no inconsistencies. Tests for: Lab wavelength errors, isotopic ratio and hyperfine structure variation. • “Positive-negative-shifter test”: Find the subset of systems that contain an anchor line, a positive shifterAND a negative shifter. Remove each type of line collectively and recalculate Da/a. • Results: subset contains 12 systems (only at high-z)No lines removed: Da/a = (-1.31  0.39)  10-5Anchors removed: Da/a = (-1.49  0.44)  10-5+ve-shifters removed: Da/a = (-1.54  1.03)  10-5-ve-shifters removed: Da/a = (-1.41  0.65)  10-5 University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  27. Variation in the fine structure constant?: Recent results and the future Radio constraints: • Hydrogen hyperfine transition at lH = 21cm. • Molecular rotational transitions CO, HCO+, HCN, HNC, CN, CS … • wH/wM  a2gP where gP is the proton magnetic g-factor. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  28. Variation in the fine structure constant?: Recent results and the future Radio constraints: • For y = a2gP, Dy/y = Dz/(1+z) for two lines; An H I 21cm line and a molecular rotational line. • Potential for much stronger contraint on a. Dy/y = 10-5 University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  29. Variation in the fine structure constant?: Recent results and the future Results to date: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  30. Variation in the fine structure constant?: Recent results and the future New (very preliminary) results: University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

  31. Variation in the fine structure constant?: Recent results and the future Conclusions: • There IS an effect in the data … but is it a varying a or just undiscovered systematic effects? • 3 independent optical samples now agree! • Must get spectra from different telescope  UVES! • Must also find more H I 21cm/mm absorbers. • Potential constraints also from combining optical spectra and H I 21cm spectra (~ 5 good candidates). • Higher-z tests: CMB and BBN constraints. University of Canterbury, New Zealand, 17/08/01 Michael Murphy, UNSW

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