Sven Zschocke

Evaluation of QCD sum rules for light vector mesons at finite density and temperature

Abstract:QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of mass parameters for the lightest vector mesons ρ, ω and φ in a strongly interacting medium. For conditions relevant for the starting experiments at HADES we find that the in-medium mass shifts of the ρ- and ω-mesons are governed, within the Borel QCD sum rule approach, by the density and temperature dependence of the four-quark condensate. In particular, the variation of the strength of the density dependence of the four-quark condensate reflects directly the decreasing mass of the ρ-meson and can lead to a change of the sign of the ω-meson mass shift as a function of the density. In contrast, the in-medium mass of the φ-meson is directly related to the chiral strange quark condensate which seems correspondingly accessible.

In-medium operator product expansion for heavy-light-quark pseudoscalar mesons

The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D -mesons and B -mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy quark and the mass of the light quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.

On the efficient computation of the quadrupole light deflection

Efficient computation of the quadrupole light deflection for both stars/quasars and solar system objects within the framework of the baseline Gaia relativity model (GREM) is discussed. Two refinements have been achieved with the goal to improve the performance of the model: - The quadrupole deflection formulas for both cases are simplified as much as possible considering the Gaia nominal orbit (only approximate minimal distances between Gaia and the giant planets were used here), physical parameters of the giant planets and the envisaged accuracy of 1µas for individual systematic effects. The recom- mended formulas are given by Eq. (40) for stars/quasars and by Eq. (81) for solar system objects. - Simple expressions for the upper estimate of the quadrupole light deflection have been found allowing, with a few additional arithmetical operations, to judge a priori if the quadrupole light deflection should be computed or not for a given source and for a given requested accuracy. The recommended criteria are given by Eq. (45) for stars/quasars and by Eq. (92) for solar system objects.

Probing the strange quark condensate by di-electrons from

Abstract:QCD sum rules predict that the change of the strange quark condensate 〈¯ss〉 in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from φ-meson decays. Due to the expansion of hadron matter in heavy-ion collisions, the φ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as an effective broadening of the di-electron spectrum in the φ region. The emerging broadening is sensitive to the in-medium change of 〈¯ss〉. This allows to probe directly in-medium modifications of 〈¯ss〉 via di-electron spectra in heavy-ion collisions at SIS energies with HADES.

\mth{\phi}

An estimate for the last unknown gauge-invariant set of QED corrections of order α2, the second-order self-energy correction, is presented utilizing the so-called sign approximation. This is able to reduce the present uncertainties in Lamb-shift predictions considerably.

-meson decays in heavy-ion collisions at SIS energies

The constituent quark number scaling of elliptic flow is studied in a nonequilibrium hadronization and freeze-out model with rapid dynamical transition from ideal, deconfined, and chirally symmetric quark-gluon plasma, to final noninteracting hadrons. In this transition a bag model of constituent quarks is considered, where the quarks gain constituent quark mass while the background bag field breaks up and vanishes. The constituent quarks then recombine into simplified hadron states, while chemical, thermal, and flow equilibrium break down one after the other. In this scenario the resulting temperatures and flow velocities of baryons and mesons are different. Using a simplified few source model of the elliptic flow, we are able to reproduce the constituent quark number scaling, with assumptions on the details of the nonequilibrium processes.

Estimate of the second order electron self energy corrections in highly charged heavy ions

Atomic binding energies are calculated at utmost precision. A report on the current status of Lamb-shift predictions for hydrogenlike ions, including all quantum electrodynamical corrections to first and second order in the fine structure constant α is presented. All relevant nuclear effects are taken into account. High-precision calculations for the Lamb shift in hydrogen are presented. The hyperfine structure splitting and the g factor of a bound electron in the strong electromagnetic field of a heavy nucleus is considered. Special emphasis is also put on parity violation effects in atomic systems. For all systems possible investigations beyond precision tests of quantum electrodynamics are considered.

Nonequilibrium hadronization and constituent quark number scaling

An algebraic method for evaluating bare nucleon matrix elements of quark operators is proposed. Thereby, bare nucleon matrix elements are traced back to vacuum matrix elements. The method is similar to the soft pion theorem. Matrix elements of two-quark, four-quark and six-quark operators inside the bare nucleon are considered.

Effects of QED and Beyond from the Atomic Binding Energy

The freeze out of a massive nucleon gas through a finite layer with time-like normal is studied. The impact of in-medium nucleon mass shift on the freeze out process is investigated. A considerable modification of the thermodynamical variables temperature, flow-velocity, energy density and particle density has been found. Due to the nucleon mass shift the freeze out particle distribution functions are changed noticeably in comparison with evaluations, which use vacuum nucleon mass.

Algebraic approach to bare nucleon matrix elements of quark operators

We discuss the status and open problems of recent calculations on QED effects in heavy few-electron ions. In particular, we examine corrections in these systems which are not of quantum electrodynamical origin but which might influence energy shifts on the same order-of-magnitude as the accuracy of present-day QED calculations.