arXiv subjects

G. Soff

Publications and source records attributed to G. Soff.

At least 19 recordsLinked to original sources

arXiv2005

Testing the time dependence of the fundamental constants in the spectra of multicharged ions

A new method for measuring a possible time dependence of the fine-structure constant ($α$) is proposed. The method is based on the level-crossing in two-electron highly-charged ions facilitating resonance laser measurements of the distance between the levels at the point of crossing. This provides an enhancement factor of about $10^{3}$ in Helium-like Europium and thus reduces the requirements for the relative accuracy of resonance laser measurements at about $10^{-12}$.

physics.atom-ph↗

arXiv2005

Apacic++ 2.0, A Parton Cascade In C++

The new version of the parton shower module APACIC++ for the SHERPA event generator framework is presented. It incorporates some features, that are specific for the consistent merging with multi-particle matrix elements at tree-level. This publication also includes some exemplary results and a short description of the upgraded class structure of APACIC++, version 2.0.

hep-ph↗

arXiv2005

Zemach and magnetic radius of the proton from the hyperfine splitting in hydrogen

The current status of the determination of corrections to the hyperfine splitting of the ground state in hydrogen is considered. Improved calculations are provided taking into account the most recent value for the proton charge radius. Comparing experimental data with predictions for the hyperfine splitting, the Zemach radius of the proton is deduced to be $1.045(16)$ fm. Employing exponential parametrizations for the electromagnetic form factors we determine the magnetic radius of the proton to be $0.778(29)$ fm. Both values are compared with the corresponding ones derived from the data obtained in electron-proton scattering experiments and the data extracted from a rescaled difference between the hyperfine splittings in hydrogen and muonium.

physics.atom-ph↗

arXiv2005

Quasi-particle model of strongly interacting matter

The successful quasi-particle model is compared with recent lattice data of the coefficients in the Taylor series expansion of the excess pressure at finite temperature and baryon density. A chain of approximations, starting from QCD to arrive at the model expressions for the entropy density, is presented.

hep-ph↗

arXiv2005

QED calculation of the n=1 and n=2 energy levels in He-like ions

We perform ab initio QED calculations of energy levels for the $n=1$ and $n=2$ states of He-like ions with the nuclear charge in the range $Z = 12$-100. The complete set of two-electron QED corrections is evaluated to all orders in the parameter $\aZ$. Uncalculated contributions to energy levels come through orders $α^3 (\aZ)^2$, $α^2 (\aZ)^7$, and higher. The calculation presented is the first treatment for excited states of He-like ions complete through order $α^2 (\aZ)^4$. A significant improvement in accuracy of theoretical predictions is achieved, especially in the high-$Z$ region.

physics.atom-ph↗

arXiv2004

Screened self-energy correction to the 2p3/2-2s transition energy in Li-like ions

We present an ab initio calculation of the screened self-energy correction for (1s)^2 2p3/2 and (1s)^2 2s states of Li-like ions with nuclear charge numbers in the range Z = 12-100. The evaluation is carried out to all orders in the nuclear-strength parameter Z α. This investigation concludes our calculations of all two-electron QED corrections for the 2p3/2-2s transition energy in Li-like ions and thus considerably improves theoretical predictions for this transition for high-Z ions.

physics.atom-ph↗

arXiv2004

The QCD equation of state near T_0 within a quasi-particle model

We present a description of the equation of state of strongly interacting matter within a quasi-particle model. The model is adjusted to lattice QCD data near the deconfinement temperature $T_c$. We compare in detail the excess pressure at non-vanishing chemical potential and its expansion coefficients with two-flavor lattice QCD calculations and outline prospects of the extrapolation to large baryon density.

hep-ph↗

arXiv2004

Predictions for multi-particle final states with SHERPA

In this contribution the new event generation framework SHERPA will be presented, which aims at a full simulation of events at current and future high-energy experiments. Some first results related to the production of weak vector bosons in association with jets at the Tevatron and the LHC will be discussed.

hep-ph↗

arXiv2004

Towards a fragmentation model for Sherpa

Some results highlighting the status of a new version of a cluster fragmentation model for the Monte Carlo event generator Sherpa are presented. In its present version this model is capable of simulating e+e- annihilation events into light-quark and gluon jets. We compare results for different multiplicity and momentum distributions to available SLD and LEP data as well as to results obtained with Herwig and Pythia.

hep-ph↗

arXiv2004

Monte Carlo models at the LHC

hep-ph↗

arXiv2004

New tools for automatic cross section calculation

In this contribution the matrix element generator AMEGIC++ will be presented. It automatically generates Feynman diagrams, helicity amplitudes, and suitable phase space mappings for processes involving multi-particle final states within the Standard Model and some of its popular extensions.

hep-ph↗

arXiv2004

Relativistic and QED corrections to the g factor of Li-like ions

Calculations of various corrections to the g factor of Li-like ions are presented, which result in a significant improvement of the theoretical accuracy in the region Z = 6-92. The configuration-interaction Dirac-Fock method is employed for the evaluation of the interelectronic-interaction correction of order 1/Z^2 and higher. This correction is combined with the 1/Z interelectronic-interaction term derived within a rigorous QED approach. The one-electron QED corrections of first in αare calculated to all orders in the parameter αZ. The screening of QED corrections is taken into account to the leading orders in αZ and 1/Z.

physics.atom-ph↗

arXiv2004

A unique parameterization of the QCD equation of state below and above T_c

We present a unique parameterization of the equation of state of strongly interacting matter in the temperature interval 0.6 T_c ... 3 T_c at μ= 0 within a quasi-particle model based on quark and gluon degrees of freedom. The extension to non-vanishing baryon-chemical potential is discussed.

hep-ph↗

arXiv2004

Gluon Emission of Heavy Quarks: Dead Cone Effect

The lowest-order induced soft gluon radiation processes of heavy quarks have been analyzed to quantify the dead cone effect. This effect is most likely expected to suppress significantly the energy loss of charm quarks passing an amorphous color-neutral deconfined medium, as has been concluded from recent experiments at RHIC.

hep-ph↗

arXiv2003

Calculation of quasi-degenerate energy levels of two-electron ions

Accurate QED calculations of the interelectron interaction corrections for the $(1s2p)2 {}^1 P_1$, $(1s2p)2 {}^3 P_1$ two-electron configurations for ions with nuclear charge numbers $10\le Z \le 92$ are performed within the line profile approach. Total energies of these configurations are evaluated. Employing the fully relativistic treatment based on the {$j$--$j$} coupling scheme these energy levels become quasi-degenerate in the region $Z\le 40$. To treat such states within the framework of QED we utilize the line profile approach. The calculations are performed within the Coulomb gauge.

physics.atom-ph↗

arXiv2003

The QCD equation of state and quark star properties

We review our quasiparticle model for the thermodynamics of strongly interacting matter at high temperature, and its extrapolation to non-zero chemical potential. Some implications of the resulting soft equation of state of quark matter at low temperatures are pointed out.

hep-ph↗

arXiv2003

Event Generator for Particle Production in High-Energy Collisions

Event generators are an indispensable tool for the preparation and analysis of particle-physics experiments. In this contribution, physics principles underlying the construction of such computer programs are discussed. Results, within and beyond the Standard Model of particle physics, obtained with a new event generator are presented. This generator is capable to describe signal processes for exotic physics and their backgrounds at electron-positron and proton-(anti)proton colliders.

hep-ph↗

arXiv2003

Renormalization-Group Analysis of the Generalized sine-Gordon Model and of the Coulomb Gas for d >= 3 Dimensions

Renormalization-group (RG) flow equations have been derived for the generalized sine-Gordon model (GSGM) and the Coulomb gas (CG) in d >= 3 of dimensions by means of Wegner's and Houghton's, and by way of the real-space RG approaches. The UV scaling laws determined by the leading-order terms of the flow equations are in qualitative agreement for all dimensions d >= 3, independent of the dimensionality, and in sharp contrast to the special case d = 2. For the 4-dimensional GSGM it is demonstrated explicitly (by numerical calculations), that the blocked potential tends to a constant effective potential in the infrared (IR) limit, satisfying the requirements of periodicity and convexity. The comparison of the RG flows for the three-dimensional GSGM, the CG, and the vortex-loop gas reveals a significant dependence on the renormalization schemes and the approximations used.

hep-th↗