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

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Outline: Motivations for varying constants, particularly the

fine structure constant =e2/c

Previous experimental limits on 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?

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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 =e2/c.

is most accessible to experimental tests of its constancy.

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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 .

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Previous limits on /: Lab. constraints Different atomic clocks tick with different

dependencies on .

The relativistic corrections are of order (Z)2.

Comparison of Hydrogen maser and Hg I clocks yielded /1.4×10-14 over 140 days (Prestage et al. 1995).

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Previous limits on /: 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”)

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 /.

1976: Shylakter first analyzed Samarium abundances from Oklo to constrain /.

1996: Damour & Dyson re-analyzed the same data to obtain a stronger constraint: /<1×10-7.

2000: Fujii et al. find /=(-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 / from the Samarium abundances. The upper limits on / might have to be weakened by a factor of more than 100! This is work in progress.

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

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

Previous limits on /: The Oklo bound

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Constraints from QSO absorption lines:

To Earth

CIVSiIVCIISiIILyem

Ly forest

Lyman limit Ly

NVem

SiIVem

Lyem

Ly SiII

Quasar

CIVem

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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.

Muana Kea (Big Mountain) in Hawaii: cold, high and dry.

W. M. Keck telescopes at 14,000 ft

Clear blue sky !

10-m (!!!) segmented primary mirror

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Constraints from QSO absorption lines:

One dimensional spectrum

Two dimensional spectrum

Echellogram

Fine absorption lines from intervening gas

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Constraints from QSO absorption lines: A Keck/HIRES doublet

Quasar Q1759+75H emission

H absorption

Metal absorption

Over 60 000 data points!

C IV doublet

C IV 1548Å C IV 1550Å

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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. C IV, Si IV and Mg II) is roughly proportional to for small /.

1976: Wolfe, Brown & Roberts first applied the AD method to intervening Mg II absorption lines.

2000: Varshalovich et al. recently obtained /=(-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 /=(-0.5 ±1.3)×10-5 (zavg=2.8).

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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!

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

The many multiplet (MM) method

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 z=0+q1x for x=(z/0)2 –1.

We must calculate q1 and measure 0.

11

21

2 Cj

) Z(electron of energy

correction icrelativist

/

Relativistic corrections for many-electron atoms:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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.

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Low-redshift data (Mg II/Fe II systems):

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

High-redshift data (damped Ly systems):

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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: z=0QSO+q1x ThAr line: z=0

ThAr+q1x

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

ThAr calibration results:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Atmospheric refraction effects:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Atmospheric refraction corrected results:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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.

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Zero isotopic ratio results:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

Variation in the fine structure constant?: Recent results and the futureOther consistency checks:

Line removal: remove each transition and fit for / again. Compare the /’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 shifter AND a negative shifter. Remove each type of line collectively and recalculate /.

Results: subset contains 12 systems (only at high-z)No lines removed: / = (-1.31 0.39) 10-5

Anchors removed: / = (-1.49 0.44) 10-5

+ve-shifters removed: / = (-1.54 1.03) 10-5

-ve-shifters removed: / = (-1.41 0.65) 10-5

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Radio constraints: Hydrogen hyperfine transition at H = 21cm.

Molecular rotational transitions CO, HCO+, HCN, HNC, CN, CS …

H/M 2gP where gP is the proton magnetic g-factor.

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

Variation in the fine structure constant?: Recent results and the futureRadio constraints: For y = 2gP,

y/y = z/(1+z) for two lines; An H I 21cm line and a molecular rotational line.

Potential for much stronger contraint on .

y/y = 10-5

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Results to date:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

New (very preliminary) results:

Michael Murphy, UNSW University of Canterbury, New Zealand, 17/08/01

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

Conclusions: There IS an effect in the data … but is it a varying

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.