QUANTUM ELECTRODYNAMICS AND PHYSICS OF THE VACUUM: QED 2000, Second Workshop

Aspects of supercritical heavy ion collisions
View Description Hide DescriptionIn collisions of very heavy ions “supercritically” strong electric fields can be created transiently. In the presence of a supercritical field the neutral vacuum state of QED becomes unstable and decays into a charged vacuum, signalled by the spontaneous emission of positrons. Consequently the emission of positrons is strongly enhanced in highZ collisions. Clear experimental signals for spontaneous positron creation are still missing and could only be expected from collisions with a prolonged time scale. We discuss possible scenarios for this to happen and indirect methods to perform a spectroscopy of superheavy quasimolecules.

Towards a Lamb shift measurement in muonic hydrogen
View Description Hide DescriptionA measurement of the Lamb shift ( energy difference) in muonic hydrogen is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the Lamb shift with 30 ppm precision and to deduce the root mean square (rms) proton charge radius with relative accuracy, 20 times more precise than presently known. The experiment is based on the availability of longlived metastable muonic hydrogen atoms in the state which has been investigated in a recent series of experiments at PSI. From the lowenergy part of the initial kinetic energy distribution of atoms we determined the fraction of longlived to be ∼1.5% for gas pressures between 1 and 64 hPa. Another analysis involving with a kinetic energy of 0.9 keV originating from quenching of thermalized via the resonant process gives the same result. This is the first direct observation of longlived atoms. The realization of the μp Lamb shift experiment involves a new lowenergy negative muon beam with entrance detectors for keVmuons, a xenon gasproportionalscintillationchamber (GPSC) read out by a microstripgaschamber (MSGC) for the detection of 2 keV Xrays, and a randomly triggered 3stage laser system providing 0.5 mJ, 7 ns laser pulses at 6.02 μm wavelength.

Precision measurements of the Casimir force using an atomic force microscope
View Description Hide DescriptionThe Casimir force results from the alteration by boundaries of the zero point electromagnetic energy. We have used the atomic force microscope to make precision measurements of the Casimir force between a large gold coated sphere and a flat plate. The complete dielectric spectrum of the metal is used in the comparison of theory to the experiment. The average statistical precision is around 1% of the forces measured at the closest separation.

QED in the worldline formalism
View Description Hide DescriptionA survey is given of applications of the “stringinspired” worldline formalism to the computation of amplitudes and effective actions in QED.

Dissipative effects in the propagation of polarized photons
View Description Hide DescriptionThe dynamics of polarized photons can be effectively modeled by means of a generalized timeevolution, that describes phenomena leading to loss of phase coherence and dissipation. High sensitive experiments, both in the laboratory and in space, will soon be able to put stringent bounds on these nonstandard effects.

Selfenergy screening in twoelectron ions
View Description Hide DescriptionThe selfenergy correction to the Coulomb part of the electronelectron interaction (selfenergy screening) is evaluated. We consider only the monopole term, which is the only one present in many cases, and the direct term. We evaluate the energy shift due to a or electron screening a or electron, for nuclear charge Z in the range A detailed comparison with other calculations is made.

Density effects in antiprotonic helium
View Description Hide DescriptionWe demonstrate that at pressures not exceeding a few bars and temperatures below 15 °K the semiclassical theory of antiprotonic helium spectral line shape agrees with the quasistatic model, and discuss the application of the latter to the shift and broadening of hyperfine transition lines.

Quantum algebraic representation of localization and motion of a Dirac electron
View Description Hide DescriptionQuantum algebraic observables representing localization in spacetime of a Dirac electron are defined. Inertial motion of the electron is represented in the quantum algebra with electron mass acting as the generator of motion. Since transformations to uniformly accelerated frames are naturally included in this conformally invariant description, the quantum algebra is also able to deal with uniformly accelerated motion.

From effective actions to actual effects
View Description Hide DescriptionThe construction of lowenergy effective actions in QED for several types of external conditions is reviewed. Emphasis is put on the application of these effective actions to a variety of physical effects which represent a manifestation of vacuum polarization. Softphoton interactions with external electromagnetic fields and/or a heat bath are described, pair production at finite temperature is discussed, and finally a glance at photonneutrino interactions is provided.

The PVLAS collaboration: Experimental search for anisotropy of the phase velocity of light in vacuum due to a static magnetic field
View Description Hide DescriptionAfter a brief description of the now operating PVLAS apparatus and of its goals, we present and discuss the preliminary experimental results obtained from the first recent measurement runs conducted with the complete setup.

Pseudoscalar production in electromagnetic fields by a Schwingerlike mechanism
View Description Hide DescriptionIn this talk I report on some recent calculations on the production of pseudoscalars from intense electromagnetic fields.

Decay of the vacuum with production of pairs in very strong magnetic fields
View Description Hide DescriptionThe statement that around some astrophysical object huge magnetic fields may exist, even larger than has been repeatedly made. In view of this fact the study of QED in presence of a magnetic field of very high intensity, both static and quasi static might find an experimental although remote counterpart. The production of pairs in these conditions is studied.

Lorentz and CPT tests in QED
View Description Hide DescriptionA theoretical framework extending QED in the context of the standard model is used to analyze a variety of Lorentz and CPT tests in atomic systems. Experimental signatures of possible Lorentz and CPT violation in these systems are investigated, and bounds are discussed.

The heatkernel coefficient and the Casimir energy of a dielectric cylinder
View Description Hide DescriptionWe calculate the heat kernel coefficients for the electromagnetic field in the background of a dielectric cylinder with non equal speeds of light inside and outside. The coefficient whose vanishing makes the vacuum energy of a massless field unique, turns out to be zero in dilute order, i.e., in order and nonzero beyond. As a consequence, the vanishing of the vacuum energy in the presence of a dielectric cylinder found by CasimirPolder summation must take place irrespectively of the methods by which it might be calculated.

A 25 T dipole pulsed magnet to study the magnetic birefringence of vacuum: the BMV project
View Description Hide DescriptionThe existence of a magnetic birefringence of vacuum is one of the most important predictions of quantum electrodynamics, which has not yet been verified. In this contribution, we present a new project, the BMV (Biréfringence Magnétique du Vide) project, a collaboration between different Grenoble, Lyon and Toulouse institutes. The proposed experimental setup, compared to previous attempts, should improve the signal level by about two orders of magnitude. Keystones of the proposed setup are a very sensitive ellipsometer and a specially designed 1.5 m long 25 T pulsed magnet, which is under development in Toulouse, France.

Electrooptical signal readout for gravitational waves resonant detectors
View Description Hide DescriptionWe describe the design and the experimental implementation of an electrooptical transduction chain conceived for the gravitational waves (GW) bar detector AURIGA. Such a transducer is qualitatively different from devices presently operating and can represent an important step towards the realization of sensitive detectors included in GW observatories.

Treatment of atomic quasidegeneracy in boundstate QED. Application to the states of Helike ions
View Description Hide DescriptionIn the case of quasidegeneracy, i.e., when there are states close in energy to the state considered, standard perturbation theory may lead to convergence problem. A typical example is the relativistic treatment of the fine structure of light heliumlike ions. In ManyBodyPerturbation Theory (MBPT) this problem can be treated by including the quasidegenerate states in an extended model space. The mixing is then treated to all orders already in the zerothorder wave function by diagonalizing an effective hamiltonian in this subspace. Only nonquasidegenerate states are treated by perturbation. Standard QED treatment of bound systems is based upon the Smatrix formalism. Here an extended model space cannot be used, the reason being that only matrix elements diagonal in energy can be determined, while the effective hamiltonian needed contains also nondiagonal elements between the states in the model space. In the present paper a modification of the boundstate QED procedure is described, based upon a covariant form of the timeevolution operator, rather than the Smatrix. In this way also elements nondiagonal in energy can be evaluated. The operator appearing in the final procedure is free from singularities, and no special procedure is needed for evaluating the socalled ModelSpace Contribution, caused by modelspace states appearing as the intermediate states. The procedure has been applied to the fine structure of heliumlike ions, and numerical secondorder QED results, including quasidegenerate levels, are presented for the first time. The formalism is closely related to MBPT and may open the possibility to combine QED and MBPT in a more systematic fashion.

The magnetic moment anomaly of the electron bound in hydrogenic ions
View Description Hide DescriptionThe measurement of the g factor of the electron bound in a hydrogenic ion is a highaccuracy test of the theory of Quantum Electrodynamics (QED) in strong fields. Here we report on the measurement of the g factor of the bound electron in hydrogenic carbon In our experiment a single ion is stored in a Penning trap. The electronic spin state of the ion is monitored via the continuous SternGerlach effect in a quantum nondemolition measurement. Quantum jumps between the two spin states (spin up and spin down) are induced by a microwave field at the spin precession frequency of the bound electron. The g factor of the bound electron is obtained by varying the microwave frequency and counting the number of spin flips. The comparison of our experimental value for the g factor of the bound electron, with the theoretical value of shows excellent agreement and confirms the recent nonperturbative calculations by T. Beier et al.

Atomic energy levels with QED and contribution of the screened selfenergy
View Description Hide DescriptionWe present an introduction to the principles behind atomic energy level calculations with Quantum Electrodynamics (QED) and the twotime Green’s function method; this method allows one to calculate an effective Hamiltonian that contains all QED effects and that can be used to predict QED Lamb shifts of degenerate, quasidegenerate and isolated atomic levels.

Neutrino scattering in a magnetic field
View Description Hide DescriptionWe examine the interaction of neutrinos with a magnetic field both within the standard model and should neutrinos possess a magnetic moment. We conclude that it is not possible to observe this interaction with magnetic fields and neutrino fluxes presently available for laboratory experiments.