Angular dependent rayleigh scattering of Mössbauer radiation on proteins

RSMR experiments with⁵⁷Fe radiation were performed on myoglobin. An areasensitive detector was employed for simultaneous angular dependent collection of the scattered quanta up to a maximum angle 2θ of 17‡. Experimental data of polycrystalline and lyophilized myoglobin are compared with computer calculations of the scattering which are based on the atomic coordinates determined by X-ray structure analysis. Special attention has been paid to the influence of coherence effects from collectively moving parts of the protein. A simple model is introduced in order to take into account these segmental motions. Our first results indicate that the sizes of collectively moving segments are comparable with spheres of about 6 å in diameter in dry myoglobin. In myoglobin crystals, where the molecules are surrounded by large hydration shells, the movements appear to be correlated in segments with sizes comparable to helices.

     

Finite size effects in stimulated laser pair production

We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e. by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs. We finally comment on the dependence of the peak positions, and in turn the effective mass, on the pulse shape.     

Nonperturbative light cone quantum field theory beyond the tree level

We demonstrate the appearance of spontaneous symmetry breaking induced by nonperturbative quantum corrections for scalar light cone quantum field theory in 1+1 dimensions. We define a light cone effective potential and obtain a second order phase transition.     

A Lorentz and gauge invariant measure of laser intensity

Focussing on null fields as simple models of laser beams we discuss the classical relativistic motion of charges in strong electromagnetic fields. We suggest a universal, Lorentz and gauge invariant measure of laser intensity and explicitly calculate and interpret it for crossed field, plane wave and vortex models.     

The vacuum structure of light-frontφ 1+1 4 -theory

We discuss the vacuum structure ofφ ⁴-theory in 1+1 dimensions quantised on the light-frontx ⁺=0. To this end, one has to solve a non-linear, operator-valued constraint equation. It expresses that mode of the field operator having longitudinal light-front momentum equal to zero, as a function of all the other modes in the theory. We analyse whether this zero mode can lead to a non-vanishing vacuum expectation value of the fieldφ and thus to spontaneous symmetry breaking. In perturbation theory, we get no symmetry breaking. If we solve the constraint, however, non-perturbatively, within a meanfield type Fock ansatz, the situation changes: while the vacuum state itself remains trivial, we find a non-vanishing vacuum expectation value above a critical coupling. Exactly the same result is obtained within a light-front Tamm-Dancoff approximation, if the renormalisation is done in the correct way.     

Radiation-Induced Cycloaddition and Polymerization in the Systems N-Ethylmalelmide-Benzene and N.-Ethylmaleimide-lsopropylbenzene

The radiolysis of the electron acceptor N-ethylmaleimide dissolved in the aromatic donors benzene and isopropyl-benzene leads to the 2:1 adduct and to a polymer fraction. The polymer fraction is composed of N-ethylmaleimide homo-polymer and N-ethylmaleimide polymer containing one or two benzene or isopropylbenzene molecules. The ratio of these products depends on the N-ethylmaleimide concentration. At low concentration adduct formation predominates, whereas at high concentration homopolymerization of N-ethylmaleimide is favored.     

Light-cone quantisation and manifestation of non-perturbative vacuum properties for scalar field theory

For a quantum field theory with interacting scalar fields treated in light-cone quantisation (LCQ) it is shown that the vacuum of the theory is always the perturbative vacuum. The fields can be split up into classical constant fields, determined by minima of the effective action, and quantum fields. The former ones replace the nontrivial vacuum expectation values of the conventionally quantised theory. When spontaneous symmetry breaking occurs, the classical fields are only determined up to symmetry transformations. This degeneracy corresponds to the degeneracy of the vacuum in the conventional approach. The effective actions of the conventional theory and LCQ are identical. Lightcone charges obey the canonical commutation relations with the fields and the canonical charge algebra relations. Ward identities and the appearance of Goldstone Bosons accompanying spontaneous symmetry breaking can be derived in analogy to the conventional case.     

On the observation of vacuum birefringence

We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized X-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years.     

The fermion condensate of the Nambu-Jona-Lasinio model in Light Cone quantisation

We investigate the incorporation of condensates in Light Cone quantisation in the frame-work of the Nambu-Jona-Lasinio model. Although it is shown that the physical and perturbative vacua are identical, a gap equation for the dynamical quark mass is obtained and chiral symmetry is dynamically broken. The complete fermion condensate is found in the perturbative vacuum. The corresponding Goldstone mode is a zero mass bound state of the Weinberg equation.