1 / 27

G. Fiorentini a : a constant that is not constant?

G. Fiorentini a : a constant that is not constant?. The QSO evidence for What else do we know about ? The Oklo natural reactor and the constancy of a Ancient meteorites, old stars and a Possible improvements about a and other “fundamental constants”. A Brief History of a.

indiya
Download Presentation

G. Fiorentini a : a constant that is not constant?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. G. Fiorentinia: a constant that is not constant? • The QSO evidence for • What else do we know about ? • The Oklo natural reactor and the constancy of a • Ancient meteorites, old stars and a • Possible improvements about • a and other “fundamental constants” G.Fiorentini

  2. A Brief History ofa • 1905 Planck: "it seems to me not completely impossible • that h has the same order of magnitude as e2/c” • 1909 Einstein :"It seems to me that we can conclude • from h=e2/c that the same modification of theory that contains • the elementary quantum e as a consequence will also contain the quantum structure of radiation” • 1911 Sommerfeld formally defines a as the ratio of the electrostatic energy of repulsion between two elementary charges, e, separated • by one Compton wavelength, to the rest energy of a single charge: G.Fiorentini

  3. Garching 2002. Measurement ofa • Neutron de-Broglie wavelength • Quantum Hall effect • ac Josephson effect • simple QED bound systems • electron anomalous magnetic moment (gold standard) • CODATA [1997] • a(ae)-1=137.03599993(52) ±4 p.p.b. G.Fiorentini

  4. Inconstant constants:Dirac ‘Large Number Hypothesis' In a letter to Nature in 1937 Dirac noted the following coincidence: ”This suggests that …large numbers are to be regarded not as constants, but as simple functions of our present epoch, expressed in atomic units. In this way we avoid the need of a theory to determine numbers of the order of 1039 “. Thus if N1 ~N2 one must have varying constants, e.g. G ~ t-1 "...the constancy of the fundamental physical constants should be checked in an experiment" - P.A.M Dirac G.Fiorentini

  5. The QSO evidence for • Absorption spectra of • diffuse clouds illuminated • by QSO suggest that • a was smaller in the past: 10-5 at 1010y ago • Assuming linear • dependence: 10-15 y-1 J.Webb et al. PRL 87(2001) Da/a=(0.72+-0.18)10-5 G.Fiorentini

  6. Alkali doublet (fine structure) P 3/2 cloud Obs. » mea4 QSO P 1/2 » mea2 S 1/2 The method • Look at absorption spectra of • diffuse clouds illuminated by QSOs • Identify two (sets of) lines, with • different a dependence,to tell both • z and a: • lobs=(1+z) lcloud • “Alkali” doublets have provided • constraints on Da: • Da /a < 10-4 • Webb et al extended the method to different atomic species, so as to obtain a larger lever arm (many multiplet method). G.Fiorentini

  7. Many multiplet method: sensitivity gain by observing lines of different species (e.g. FeII and Mg II). Lines are in quite different regions: one needs careful checks for possible miscalibrations The many multiplet results G.Fiorentini

  8. Summary of information on da/dt t, z connected with Ho=70Km/s/Mpc (WM,WL)=(0.3,0.7) G.Fiorentini

  9. Remarks • Only positive claim from QSO • Possibly in conflict with Oklo data • However: • -non linear evolution of a? • -is a space dependent? • -compensation between changes of a and of other “fundamental constants”? • Radioactive dating of solar system (and/or globular clusters stars) can reach sensitivity comparable to QSO G.Fiorentini

  10. Atomic Clocks • Compare clocks, with frequencies which depend differently on a, and look for change in relative clock rates. • Best comparison involves H-maser ( HFS of H, n1µa4 )and Hg+ atomic clock (HFS of Hg+, n2µa4 Frel(aZ) ) : • d/dt ln(n1 / n2 ) =(dlna/dt) d/da ln Frel • Measurements over 140 days have given: • (da/dt)/a < 3.7 10-14 y-1 (Prestage et al PRL 74(1995)3511) • Future measurements should reach 10-16 y-1 and be capable of testing the QSO claim. G.Fiorentini

  11. Atomic Clocks in space Ultimate limit for frequency measurement is observation time. Cold atoms in lab fall due to gravity Atoms in free fall don’t fall, i.e. go to space. Comparison between atomic clocks in the Space Station could reach a sensitivity to (da/dt)/a =10-16 y-1 and be capable of testing the QSO claim (ACES: www.cnes.fr/activites/connaissance/physique/aces/1sommaire_aces.htm) G.Fiorentini

  12. ACESAtomic Clocks Ensemble in Space • ACES has been approved to fly on the International Space Station as an external payload, starting from 2002 for a period of one and a half years. • It consists of the following key elements: • A laser cooled atomic clock "PHARAO" _ contributed to the project by France, • A Hydrogen Maser _ contributed by Switzerland, • A laser link for optical transfer of time and frequency _ contributed by France • A microwave link for transfer of time and frequency _ contributed by ESA Fundamental physics: -general relativity tests -stability of fundamental constants Applications: -Navigation and positioning - New concepts for higher performance GPS systems. - Geodesy with millimetric precision. - Precise tracking of remote space probes. -Time and frequency metrology - Comparing and synchronising clocks over intercontinentaldistances to an accuracy of 10-16. www.cnes.fr/activites/connaissance/physique/aces/1sommaire_aces.htm) G.Fiorentini

  13. The Oklo phenomenon • A natural fission reactor • which released about 20 KW • for 700 000 years • about 1.8 Gyr ago • Oklo gives the most strict bound : • Da/a<10-7 • (da/dt)/a <6 10-17 G.Fiorentini

  14. Footprints of natural fission • (U235/U238)World= 0.7 % • (U235/U238)OKlo= 0.4 % . • Who has stolen U235? • U235/U238» 3 % 2Gyr ago, • enough for a water moderated reactor. • Abundances of Rare Earths Isotopes at Oklo are similar to those produced by fission. G.Fiorentini

  15. Garching 2002. What do we learn from Oklo ? • Characteristic isotope abundances are due to large sabs of thermal neutrons (e.g.: n+149Sm-> 150Sm+g) • sabs large due to resonances near thermal energy*, • for 149Sm Eres= 97.3 meV today • At reactor time this resonance was efficient too: • DEres <0.1 eV • Electromagnetism contributes to nuclear energy levels: • Ecou» a/rnuc» MeV. • Tiny changement of a would spoil the resonance efficiency: • ïDa/aï < 10-7 * KT = 50 meV at T=600 K G.Fiorentini • Shlyakhter Nature (1976), DysonDamour NPB (1996) Fujii et al NP(2000)

  16. Garching 2002. Oklo and nuclearclocks • One is comparing nuclear reaction rates now and at Oklo time. • Essentially one is comparing two nuclear clocks • These are sensitive both to e.m and nuclear forces: Ecou» a/rnuc • (Warning: compensation between Da and Drnuc ?) • Other nuclear clocks are available in nature (reaction rates in stars, nuclear lifetimes…) G.Fiorentini

  17. Garching 2002. Nuclear lifetimes and a • Nuclear lifetimes can depend strongly on a • e.g.: alpha decay LU238» exp[-104a] • Merit factor for sensitivity to • change of a is: • s= dln L / dln a • The highest sensitivity is for • 187Re->187Os+e+ , due to • the very small Q value (2,5 KeV), which depends on the Coulomb contribution to nuclear levels, which depends on a. • Dyson 1972 G.Fiorentini

  18. Radioactive datings of the solar system • The age of old meteorites can be determined • by means of different radioactive methods • (e.g.: U/Th almost insensible to Da, whereas Re/Os strongly sensitive to Da) • Each dating determines x= age <Dec_Rate>met. • One determines age by one method and use the measured Os/Re value to derive a geochemical value of Re decay rate • Geochemistry Þ <L>met. =(2.40±0.02)10-11 y-1 • Lab.measurement Þ Lpres =(2.36±0.04)10-11 y-1 • Comparison Þ [apres- <a>met ]/ apres= (1 ± 1)10-6 • + linear evol. Þ = (0.4±0.5)10-15 y-1 Sensitivityworse than Oklo, however comparable to QSO G.Fiorentini

  19. 12C synthesis • Our existence relies on a nuclear accident, • a suitably placed 12C excited level which • makes carbon synthesis efficient in stars • at kT»10KeV, through • a+a+a-> 12C* -> 12C +g • We measure now: dm = m12*-3ma =379.5KeV • dmcontains a Coulomb contribution Ecou» a/rnuc . • We see 12C in old stars. This implies the resonance has not moved by more than kT=10KeV--->ïDa/aï < 10-2 • Conceptually, the same argument as Oklo. • Sensitivity is worse than Oklo, due to larger kT • However it probes older times, t» 10 Gyr G.Fiorentini

  20. Radioactive dating of old stars • Radioactive dating has been extended • to the oldest stars in the Galaxy, • essentially by means of Th decay. • Recently measurement of a stellar age • by means of U decay has been obtained • Significant improvement, since U decays • faster and initial abundance is better estimated: • TCayrel = (12.5 +- 3)Gyr • This nuclear clock depends on a. Cayrel et al. Nature 409(2001) G.Fiorentini

  21. Measurement of stellar age from U decay Cayrel et al. Nature 409(2001) G.Fiorentini

  22. Comparison of stellar clocks • The evolution of globular • cluster provides a standard • chronometer of the Galaxy. • This method is substantially • insensitive to a changes. • The agreement with the • nuclear clock within • (errors of) 3 Gyr implies: • Da/a< 10-3 at t=12Gyr G.Fiorentini

  23. Change a Þ change BE Þ change recomb.time Þ change z(last scat.) Þ change l(peak) Garching 2002. a and the CMB A lower a seemed preferred by CMB. See however update... G.Fiorentini

  24. a and BBN Change a ß change mn-mp ß change Nn at freezeout ß change 4He ß Da/a<10-2 G.Fiorentini

  25. Garching 2002. a , CMB and BBN : update Astro-ph/0102144 BBN: CMB: G.Fiorentini

  26. a is not alone • The idea that several “fundamental constants” can vary on cosmological scales goes back to Dirac (1937) • Time variations of “fundamental Constants”are natural in theories with extra dimensions (see Marciano, Dvali, Zaldarriaga…) • GUT require that an evolution of aem be accompanied by changes of ai, or GUT is occasional. G.Fiorentini

  27. Concluding remarks • Actually unification requires changes of aem to be accompanied by a much stronger change in strong interaction parameters (Calmet, Fritsch, Langacker….) DLqcd/Lqcd»40 Daem/aem • Several consequences, since Mp,nµLqcd Mp2µLqcd • Signal/bounds on daem/dt give info on other interactions • Analysis have to incorporate DLqcd as well asDaem • Dedicated experiments are needed The constancy of the fundamental physical constants should be checked in an experiment" - P.A.M Dirac (1937) G.Fiorentini

More Related