arXiv subjects

Boris Krippa

Publications and source records attributed to Boris Krippa.

22 records · Page 2Linked to original sources

arXiv1997

Chiral symmetry and mixing of axial and vector correlators in matter

The effect of mixing of the vector and axial vector correlation functions in the nuclear medium arising from the interaction of nuclear pions with corresponding interpolating currents is considered. It is shown that the mass difference between $ρ$ and $a_1$ meson gets smaller with the increase of the nuclear density reflecting the phenomena of partial restoration of chiral symmetry whereas the absolute values of meson masses may both decrease and increase in nuclear medium depending on the model used for the phenomenological spectral density.

hep-ph↗

arXiv1996

Determination of pion-baryon coupling constants from QCD sum rules

We evaluate the pi-N-N, pi-Sigma-Sigma and pi-Sigma-Lambda coupling constants using QCD sum rules based on pion-to-vacuum matrix elements of correlators of two interpolating baryon fields. The parts of the correlators with Dirac structure k-slash gamma_5 are used, keeping all terms up to dimension 5 in the OPE and including continuum contributions on the phenomenological side. The ratios of these sum rules to baryon mass sum rules yield stable results with values for the couplings of g_{pi NN}=12+/-5, g_{pi Sigma Sigma}=7+/-4 and g_{pi Sigma Lambda}=6+/-3. The sources of uncertainty are discussed.

hep-ph↗

arXiv1996

Chiral symmetry and QCD sum rules for the nucleon mass in matter

The quark condensate in nuclear matter contains a term of order $ρm_π$, arising from the contribution of low-momentum virtual pions to the $πN$ sigma commutator. Standard treatments of QCD sum rules for a nucleon in matter generate a similar term in the nucleon effective mass, although this is inconsistent with chiral perturbation theory. We show how an improved treatment of pionic contributions on the phenomenological side of the sum rules can cancel out this unwanted piece. Our results also show that factorisation ansatz for the four-quark condensate cannot be valid in matter.

hep-ph↗

arXiv1996

Determination of the pion-nucleon coupling constant from QCD sum rules

We evaluate the $πN$ coupling constant using a QCD sum rule based on the pion-to-vacuum matrix element of the correlator of two interpolating nucleon fields. The part of the correlator with Dirac structure $k\llap/γ_5$ is used, keeping all terms up to dimension 5 in the OPE and including continuum contributions on the phenomenological side. The ratio of this sum rule to the nucleon sum rule involving condensates of odd dimension yields stable results with values of $g_{πN}$ in the range $12\pm 5$. The sources of uncertainty are discussed.

hep-ph↗