arXiv subjects

Th. Gutsche

Publications and source records attributed to Th. Gutsche.

40 records · Page 3Linked to original sources

arXiv2000

Strange quark polarization of the nucleon: A parameter-independent prediction of the chiral potential model

We perform a one-loop calculation of the strange quark polarization ($Δs$) of the nucleon in a SU(3) chiral potential model. We find that if the intermediate excited quark states are summed over in a proper way, i.e., summed up to a given energy instead of given radial and orbital quantum numbers, $Δs$ turns out to be almost independent of {\em all} the model parameters: quark masses, scalar- and vector-potential strengths. The contribution from the quark-antiquark pair creation and annihilation ``$Z$'' diagrams is found to be significant. Our numerical results agree quite reasonably with experiments and lattice QCD calculations.

hep-ph↗

arXiv2000

Positive strangeness contribution to the nucleon magnetic moment in a relativistic chiral potential model

The strangeness contribution to the nucleon magnetic moment is calculated at the one-loop level in a relativistic SU(3) chiral potential model and is found to be {\em positive}, that is, with an {\em opposite} sign to the nucleon strangeness polarization. It is the ``Z'' diagram that violates the usual relation between spin and magnetic moment. The positive value is due to the contribution from the intermediate excited quark states, while the intermediate ground state gives a negative contribution. Our numerical results agree quite well with the new measurement of the SAMPLE Collaboration.

hep-ph↗

arXiv2000

Renormalization of quark axial current in the chiral potential model

Non-conserved composite operators like the quark axial current have divergent matrix elements therefore must be renormalized. We explore how this can be done in quark model calculations where the systematic procedure of dimensional regularization and minimal subtraction is not applicable. We propose a most natural and convenient regularization scheme of cutting the intermediate quark states over which we sum in loop diagram calculations at a certain energy. We show that this scheme works perfectly for the quark axial current and we obtain the quark spin contribution to the proton spin: $Δ_u=0.82$, $Δ_d=-0.43$, $Δ_s=-0.10$, which is in excellent agreement with experiments.

hep-ph↗

arXiv1999

Direct Test of the Scalar-Vector Lorentz Structure of the Nucleon- and Antinucleon-Nucleus Potential

Quantum Hadrodynamics in mean field approximation describes the effective nucleon-nucleus potential (about -50 MeV deep) as resulting from a strong repulsive vector (about 400 MeV) and a strong attractive scalar (about -450 MeV) contribution. This scalar-vector Lorentz structure implies a significant lowering of the threshold for $p\bar{p}$ photoproduction on a nucleus by about 850 MeV as compared to the free case since charge conjugation reverses the sign of the vector potential contribution in the equation of motion for the $\bar{p}$ states. It also implies a certain size of the photon induced $p\bar{p}$ pair creation cross section near threshold which is calculated for a target nucleus $^{208}$Pb. We also indicate a measurable second signature of the $p\bar{p}$ photoproduction process by estimating the increased cross section for emission of charged pions as a consequence of $\bar{p}$ annihilation within the nucleus.

nucl-th↗