Observational Bounds on Fine-Structure Constant Variations  

In General > s.a. fine-structure constant.
* Idea: Support for the possibility is mixed; Absorption spectra of interstellar matter have led to claims both for and against variations of α.
* Methods: Astrophysical observations determine shifts in α by comparing the spectra of light from 3 to 10 billion years ago to those from current laboratory measurements; Atomic clock measurements compare the frequencies of two atomic transition lines, either on the same atom or on different atoms, over time.
* History: At one point Eddington asserted that the fine structure constant was, for numerological reasons, exactly 1/137.
* 1997: Δ(gpα2)/(gpα2) < 5 × 10–6 at z = 0.25, 0.68; Δα/α ≤ 2 × 10–4 for atoms at z > 1.
* 2000: α·/α ≤ 3.5 × 10–15/yr out to t0t ~ 4.8 Gyr.
* 2001: Δα/α ~ 10–5 over 12 × 109 yr (4.1-σ effect), from metal absorption line spacings in gas clouds, propto α2.
* 2003: Δα/α < (–2 ± 1.2) × 10–4 for quasars with 0.16 < z < 0.80, from O III emission lines.
* 2004: Δα/α = (–0.06 ± 0.06) × 10–5 for Mg II at 0.4 < z < 2.3, and results for Si IV at 1.59 < z < 2.92, consistent with 0; α·/α ≤ 2.0 × 10–15/yr (1-σ, present).
* 2005: There are still discrepancies, with the deepest data showing an increase by 6 × 10–9 over 12 × 1012 yr, and other data consistent with no change; One possibility is that α varied earlier and no longer varies; Δα/α = (–0.07 ± 0.84) × 10–6 for Fe II at z = 1.15.
* 2006: Still no agreement on effect; Δα/α = (0.05 ± 0.24) × 10–6 at z = 1.1508.
* 2007: Change between recombination (1012 < z < 1115) and now is –0.039 < Δα < 0.010 at 95% c.l., from WMAP3 data.
* 2008: Researchers at NIST have concluded that α is not changing to within 1.6 × 10–17 per year.
* 2009: WMAP5 data give α/α0 = 0.987 ± 0.012 at 68% c.l., and 1.001 ± 0.007 at 68% including H0 constraints from HST.
* 2010: Data from the natural Oklo reactor give α·/α ≤ 5.0 × 10–18/yr.
* 2012: Evidence for a dipole pattern with amplitude (1.1 ± 0.2) × 10–6/GLyr proportional to lookback time, significant at the 4.2-σ confidence level.
* 2014: No significant change seen in the redshift range z = 0.7 – 1.5.
* 2016: No significant change seen in the redshift range z = 1.0 – 2.4.
@ General references: Kraiselburd et al A&A(13)-a1307 [update]; Alves et al PLB(17)-a1704 [upcoming experiments].
@ Spectral lines: Webb & al PRL(99)ap/98, PRL(01)ap/00; Varshalovich et al PS(01)phy/00; Murphy et al MNRAS(01)ap/00, ASS(03)ap/02-proc [details], MNRAS(03)ap; Darling PRL(03) [OH microwave transitions]; Webb pw(03)apr [rev]; Bahcall et al ApJ(04)ap/03 [O III]; Srianand et al PRL(04)ap, criticism Murphy et al PRL(07)-a0708; Angstmann et al PRA(04)ap [bounds]; Chand et al A&A(04)ap [Mg II], A&A(05)ap/04 [Si IV]; Peik et al PRL(04); Dzuba & Flambaum PRA(05)ap; Grupe et al AJ(05)ap; Levshakov et al IAU(05)ap-in [Fe II, z = 1.15, SIDAM]; Chand et al A&A(06)ap; Murphy et al MNRAS(08)ap/06; Khatri & Wandelt PRL(07)ap + pw(07)mar, comment Flambaum & Porsev a1004, reply PRL(10)-a1007 [effect on 21-cm radiation]; King et al a0910-proc [Monte Carlo methods]; Albareti et al MNRAS(15)-a1501 [13k quasar spectra at z < 1].
@ Spectral lines, no evidence: Drinkwater et al IAP-ap/97, MNRAS(98)ap/97, Carilli et al PRL(00)ap + pn(00)dec [21-cm H line]; Levshakov LNP-ap/03; Quast et al A&A(04)ap/03 [Fe II]; Molaro et al IAU(05)ap, EPJST(08)-a0712 [Fe II]; Lentati et al MNRAS(13)-a1211; Leefer et al PRL(13) [using atomic dysprosium]; Songaila & Cowie ApJ(14)-a1406; Huntemann et al PRL(14), Godun et al PRL(14) [atomic clock measurements]; Murphy et al MNRAS(16)-a1606 [Zn and Cr quasar absorption lines]; Murphy et al MNRAS-a1708.
@ From cmb: Hannestad PRD(99)ap/98; Kaplinghat et al PRD(99); Avelino et al PRD(01)ap [bounds]; Martins ap/02-proc [bounds]; Rocha et al NAR(03)ap-proc, MNRAS(04)ap/03 [WMAP, bounds]; Ichikawa et al PRD(06)ap; Stefanescu NA(07)-a0707 [WMAP 3-year data]; Mosquera et al A&A(08)-a0707 [and Bekenstein model]; Scóccola et al PLB(08)-a0809, Nakashima et al PTP(08)-a0810, Scóccola et al a0910-proc [WMAP 5-year data]; Menegoni et al PRD(09)-a0909; Nakashima et al JCAP(10).
@ Lab experiments: Livio & Stiavelli ApJL(98)ap; Marion et al PRL(03)phy/02 [atomic fountain clock]; Nguyen et al PRA(04) [dysprosium lines]; Barrow & Shaw PRD(08)-a0806 [stronger constraints]; news quanta(18)apr [atomic clocks and search for dark matter].
@ Oklo reactor: Lamoreaux & Torgerson PRD(04); Onegin MPLA(12)-a1010; Davis & Hamdan PRC(15)-a1503; Hamdan & Dabis a1510-conf.
@ In gravitational fields: Berengut et al PRL(13)-a1305 [bounds on variation]; Bambi JCAP(14)-a1308, Preval et al a1410-proc [strong fields]; Bainbridge et al Univ(17)-a1702-proc [white dwarf stars].
@ Related topics: Fujii & Iwamoto PRL(03) [Re/Os decay rate], MPLA(05) [dating meteorites]; Centurión et al a0910-proc [calibration issues]; Galli PRD(13)-a1212 [from galaxy cluster X-ray emission]; Onegin a1412; Holanda et al JCAP(16)-a1510 [galaxy clusters]; > s.a. tests of the equivalence principle.

Spatial Variation
* 2016: There are indications of a spatial variation of α at a level of a few parts per million, with a dipole providing a statistically good fit to the data.
@ References: Webb et al PRL(11)-a1008 + news tb(11)oct, sci(11)nov; King et al MNRAS(12)-a1202 [evidence for dipole pattern]; Berengut et al A&A(12)-a1203; Olive et al PRD(12)-a1204 [and dilatonic domains]; Cameron & Pettitt a1207/MNRAS, a1309/MNRAS [skeptical interpretation]; Pinho & Martins PLB(16)-a1603, de Martino et al a1612-conf [updated constraints].

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