Interest in the variation of fundamental constants has recently been stimulated by claims that the fine structure constant, α, was smaller in the past. Physicists are investigating whether α is currently varying using a number of methods including atomic clock experiments and quasar absorption spectra. To date atomic clock experiments have not reached the same level of precision as the quasar results but the precision to which transition frequencies are being measured is increasing dramatically and very soon atomic clock experiments based on Earth will be able to rival or surpass the quasar results. In order to relate the change in transition frequencies to a variation of α accurate calculations of relativistic effects in atoms and their dependence upon α are needed. Other effects, such as the small shift of transition frequencies due to blackbody radiation also need to be accounted for. In this thesis we perform accurate calculations of the dependence of transition frequencies in two-valence-electron atoms and ions on a variation of α. The relativistic Hartree-Fock method is used with many-body perturbation theory and configuration interaction methods to calculate transition frequencies. We also consider transitions with an enhanced sensitivity to α variation. In particular, narrow lines that correspond to atomic transitions between close lying, long-lived atomic states of different configurations. The small transition frequency, coupled with differences in the electron structure ensures a strong enhancement of the relative frequency change compared to a possible change in α . We also show that using the modified form of the Dirac Hamiltonian, as suggested by Bekenstein, does not affect the analysis of the quasar data pertaining to a measurement of α variation, nor does it affect atomic clock experiments. Finally we have performed calculations of the size of the frequency shift induced by a static electric field on the clock transition frequencies of the hyperfine splitting in Y b+, Rb, Cs, Ba+, and Hg+. The calculations are used to find the frequency shifts due to blackbody radiation which are needed for accurate frequency measurements and improvements of the limits on variation of α. Our result for Cs [??v/=E2 = -2:26(2) x 10-10Hz/(V/m)2] is in good agreement with early measurements and ab initio calculations. We present arguments against recent claims that the actual value might be smaller. The difference (~ 10%) is due to the continuum spectrum in the sum over intermediate states.

This thesis addresses the issue of the time variability of the fine structure constant, alpha. Recent claims of a varying alpha are set against the established standards of quantum electrodynamical theory and experiments. A study of the feasibility of extracting data on the time dependence of alpha using particles in Penning traps is compared to the results obtained by existing methods, including those using astrophysical data and those obtained in atomic clock experiments. Suggestions are made on the nature of trapped particles and the trapping fields.

No description available.

A single electron in a quantum cyclotron provides the most precise measurement of the electron magnetic moment, given in units of the Bohr magneton by g/2 = 1.001 159 652 180 73 (28) [0.28 ppt]. The most precise determination of the fine structure constant comes from combining this measurement with Standard Model theory, yielding \(\alpha^{-1} = 137.035 999 173 (34)\) [0.25 ppb], limited by the experimental uncertainty of the electron g-value. The most stringent test of CPT symmetry in leptons comes from comparing the electron and positron magnetic moments, limited by the positron uncertainty at 4.2 ppt. A new high-stability apparatus has been built and commissioned for improved measurements of the electron and positron magnetic moments, a greatly improved test of lepton CPT symmetry, and an improved determination of the fine structure constant. These new measurements require robust positron loading from a retractable radioactive source that is small enough to avoid compromising the high-precision environment of our experiment. The design and implementation of such a scheme is a central focus of this work. Robust positron loading at a rate of \(1-2 e^+/min\) from a \(6.5 \mu Ci^{22}Na\) source has been demonstrated. / Physics

Presently, Planck’s constant is a fundamental constant that can not be derived from other onstants. Assis developed a model based on an extended Weber-type potential energy, that allows calculating gravitational-type forces from neutral oscillating electric dipoles. Here we show that the maximum possible point-mass in his model equals the Planck mass which allows us to derive Planck’s constant and the fine-structure constant. We match the exact order of magnitude only requiring a pre-factor that is present in all Weber-type theories and has to be determined empirically. This classical model allows to link electromagnetic, gravitational and quantum properties with one approach.

Presently, Planck’s constant is a fundamental constant that can not be derived from other onstants. Assis developed a model based on an extended Weber-type potential energy, that allows calculating gravitational-type forces from neutral oscillating electric dipoles. Here we show that the maximum possible point-mass in his model equals the Planck mass which allows us to derive Planck’s constant and the fine-structure constant. We match the exact order of magnitude only requiring a pre-factor that is present in all Weber-type theories and has to be determined empirically. This classical model allows to link electromagnetic, gravitational and quantum properties with one approach.

Für verschiedene Richtgrößen, die untersucht werden, um Hinweise auf Neue Physik jenseits des Standardmodells der Teilchenphysik zu finden, stellt die Gitter-QCD stellt derzeit den einzigen Ab-initio-Zugang für die Berechnung von nichtperturbativen hadronischen Beiträgen dar. Zu diesen Observablen gehören die anomalen magnetischen Momenten der Leptonen und das Laufen der elektroschwachen Kopplungskonstanten. Wir bestimmen den führenden QCD-Beitrag zum anomalen magnetischen Moment des Myons mit Hilfe einer Gitter-QCD-Rechnung auf Ensemblen, die Nf=2+1+1 dynamische Twisted-Mass-Fermionen berücksichtigen. Durch die Betrachtung aktiver up, down, strange and charm Quarks können erstmalig Gitter-QCD-Daten für die Myonanomalie direkt mit phänomenologischen Resultaten verglichen werden, da letztere bei der derzeitigen Genauigkeit sensitiv auf die ersten beiden Quarkgenerationen sind. Unlängst wurde darauf hingewiesen, dass es auch möglich sein könnte Beiträge Neuer Physik durch verbesserte Messungen der anomalen magnetischen Momente des Elektrons und des Tauons nachzuweisen. Aus diesem Grund berechnen wir auch deren führende QCD-Beiträge, was gleichzeitig eine Überprüfung des Wertes für das Myon liefert. Zusätzlich nutzen wir die gewonnenen Daten, um den führenden hadronischen Beitrag zum Laufen der Feinstrukturkonstante zu berechnen. Darüber hinaus zeigen wir, dass sogar für den schwachen Mischungswinkel der führende QCD-Beitrag mit Hilfe dieser Daten berechnet werden kann. Dadurch identifizieren wir eine neue grundlegende Observable für die Suche nach Neuer Physik, deren hadronische Beiträge mit Hilfe der Gitter-QCD beschafft werden können. Mit den Resultaten dieser Arbeit ist es uns gelungen ungeeignete Herangehensweisen der phänomenologisch notwendigen Flavourseparation auszuschließen und somit direkt die derzeit präziseren phänomenologischen Bestimmungen dieser bedeutsamen physikalischen Größe zu unterstützen. / For several benchmark quantities investigated to detect signs for new physics beyond the standard model of elementary particle physics, lattice QCD currently constitutes the only ab initio approach available at small momentum transfers for the computation of non-perturbative hadronic contributions. Among those observables are the lepton anomalous magnetic moments and the running of the electroweak coupling constants. We compute the leading QCD contribution to the muon anomalous magnetic moment by performing lattice QCD calculations on ensembles incorporating Nf=2+1+1 dynamical twisted mass fermions. Considering active up, down, strange, and charm quarks, admits for the first time a direct comparison of the lattice data for the muon anomaly with phenomenological results because both the latter as well as the experimentally obtained values are sensitive to the complete first two generations of quarks at the current level of precision. Recently, it has been noted that improved measurements of the electron and tau anomalous magnetic moments might also provide ways of detecting new physics contributions. Therefore, we also compute their leading QCD contributions, which simultaneously serve as cross-checks of the value obtained for the muon. Additionally, we utilise the obtained data to compute the leading hadronic contribution to the running of the fine structure constant, which enters all perturbative QED calculations. Furthermore, we show that even for the weak mixing angle the leading QCD contribution can be computed from this data. In this way, we identify a new prime observable in the search for new physics whose hadronic contributions can be obtained from lattice QCD. With the results obtained in this thesis, we are able to exclude unsuitable phenomenologically necessary flavour separations and thus directly assist the presently more precise phenomenological determinations of this eminent quantity.