Accurate spline solutions of the Dirac equation with parity-nonconserving potential

The complete system of the B-spline solutions for the Dirac equation with the parity-nonconserving (PNC) weak interaction effective potential is obtained. This system can be used for the accurate evaluation of the radiative corrections to the PNC amplitudes in the multicharged ions and neutral atoms. The use of the scaling procedure allows for the evaluation of the PNC matrix elements with relative accuracy $10^{-7}$.Comment: 7 page

Pion production from a critical QCD phase

A theoretical scheme which relates multiparticle states generated in ultrarelativistic nuclear collisions to a QCD phase transition is considered in the framework of the universality class provided by the 3-D Ising model. Two different evolution scenarios for the QGP system are examined. The statistical mechanics of the critical state is accounted for in terms of (critical) cluster formation consistent with suitably cast effective action functionals, one for each considered type of expansion. Fractal properties associated with these clusters, characterizing the density fluctuations near the QCD critical point, are determined. Monte-Carlo simulations are employed to generate events, pertaining to the total system, which correspond to signals associated with unconventional sources of pion production

The Crystallography of Color Superconductivity

We develop the Ginzburg-Landau approach to comparing different possible crystal structures for the crystalline color superconducting phase of QCD, the QCD incarnation of the Larkin-Ovchinnikov-Fulde-Ferrell phase. In this phase, quarks of different flavor with differing Fermi momenta form Cooper pairs with nonzero total momentum, yielding a condensate that varies in space like a sum of plane waves. We work at zero temperature, as is relevant for compact star physics. The Ginzburg-Landau approach predicts a strong first-order phase transition (as a function of the chemical potential difference between quarks) and for this reason is not under quantitative control. Nevertheless, by organizing the comparison between different possible arrangements of plane waves (i.e. different crystal structures) it provides considerable qualitative insight into what makes a crystal structure favorable. Together, the qualitative insights and the quantitative, but not controlled, calculations make a compelling case that the favored pairing pattern yields a condensate which is a sum of eight plane waves forming a face-centered cubic structure. They also predict that the phase is quite robust, with gaps comparable in magnitude to the BCS gap that would form if the Fermi momenta were degenerate. These predictions may be tested in ultracold gases made of fermionic atoms. In a QCD context, our results lay the foundation for a calculation of vortex pinning in a crystalline color superconductor, and thus for the analysis of pulsar glitches that may originate within the core of a compact star.Comment: 41 pages, 13 figures, 1 tabl

Bremsstrahlung in intermediate-energy nucleon reactions within an effective one-boson exchange model

Within a covariant effective one-boson exchange model for the $T$ matrix of $NN$ interactions we present detailed calculations of bremsstrahlung cross sections for proton - proton and proton - neutron reactions at beam energies in the 1 GeV region. Besides pure bremsstrahlung processes we consider photons from $\Delta$ decays and contributions from the $\eta \to \gamma \gamma$ process. At beam energies above 700 MeV the $\Delta$ decay channel dominates the spectra at large photon energies, where the interference between non-resonance processes and the $\Delta$ decay channel becomes also important. Low energy photons stem from pure bremsstrahlung processes. The available experimental data at 730 MeV beam energy is well described. We extrapolate the model down to 280 MeV, where more detailed experimental data exist, and find agreement with angular distributions.Comment: 20 pages with 10 figures, to be published in Nucl. Phys.

Mass-Induced Crystalline Color Superconductivity

We demonstrate that crystalline color superconductivity may arise as a result of pairing between massless quarks and quarks with nonzero mass m_s. Previous analyses of this phase of cold dense quark matter have all utilized a chemical potential difference \delta\mu to favor crystalline color superconductivity over ordinary BCS pairing. In any context in which crystalline color superconductivity occurs in nature, however, it will be m_s-induced. The effect of m_s is qualitatively different from that of \delta\mu in one crucial respect: m_s depresses the value of the BCS gap \Delta_0 whereas \delta\mu leaves \Delta_0 unchanged. This effect in the BCS phase must be taken into account before m_s-induced and \delta\mu-induced crystalline color superconductivity can sensibly be compared.Comment: 12 pages, 4 figures. v2: very small change onl

Breached Pairing Superfluidity at Finite Temperature and Density

A general analysis on Fermion pairing at finite temperature and density between different species with mismatched Fermi surfaces is presented. Very different from the temperature effect of BCS phase, the recently found breached pairing phase resulted from density difference of the two species lies in a region with calabash-like shape in the $T-\mu$ plane, and the most probable temperature for the new phase's creation is finite but not zero.Comment: 5 papes, 5 figures. Comments are welcome to [email protected]

A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions

We have developed a versatile software package for the simulation of di-electron production in $pp$ and $dp$ collisions at SIS energies. Particular attention has been paid to incorporate different descriptions of the Dalitz decay $\Delta \to N e^+e^-$ via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process $NN \to NN e^+e^-$ based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and the design of forthcoming experiments

Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering

We investigate the possibility of identifying an explicit pionic component of the nucleon through measurements of polarized $\Delta^{++}$ baryon fragments produced in deep-inelastic leptoproduction off polarized protons, which may help to identify the physical mechanism responsible for the breaking of the Gottfried sum rule. The pion-exchange model predicts highly correlated polarizations of the $\Delta^{++}$ and target proton, in marked contrast with the competing diquark fragmentation process. Measurement of asymmetries in polarized $\Lambda$ production may also reveal the presence of a kaon cloud in the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in Zeit. Phys.

Polarization observables in the reaction NN→NNΦNN \to NN \Phi

We study the reaction $NN \to NN \Phi$ slightly above the threshold within an extended one-boson exchange model which also accounts for $uud$ knock-out. It is shown that polarization observables, like the beam-target asymmetry, are sensible quantities for identifying a $s \bar s$ admixture in the nucleon wave function on the few per cent level.Comment: 11 LaTeX pages including 4 ps figure

The 3-D O(4) universality class and the phase transition in two-flavor QCD

We determine the critical equation of state of the three-dimensional O(4) universality class. We first consider the small-field expansion of the effective potential (Helmholtz free energy). Then, we apply a systematic approximation scheme based on polynomial parametric representations that are valid in the whole critical regime, satisfy the correct analytic properties (Griffiths' analyticity), take into account the Goldstone singularities at the coexistence curve, and match the small-field expansion of the effective potential. From the approximate representations of the equation of state, we obtain estimates of several universal amplitude ratios. The three-dimensional O(4) universality class is expected to describe the finite-temperature chiral transition of quantum chromodynamics with two light flavors. Within this picture, the O(4) critical equation of state relates the reduced temperature, the quark masses, and the condensates around T_c in the limit of vanishing quark masses.Comment: 19 pages, 5 fig