TY - JOUR
T1 - Nuclear aspects of chiral symmetry
AU - Weise, W.
N1 - Funding Information:
The non-perturbative QCD vacuum is characterised by condensates of quarks and gluons. The gluon condensate is a measure of scale invariance breaking in QCD, while the quark condensate < qq > is the order parameter of spontaneous chiral symmetry breaking. There is general agreement that the ma~:nitude of < ~q > decreases in a dense nuclear environment, indicating the tendency towards chiral symmetry restoration. One expects that !< qq >l drops by about 1/3 of its vacuum value already at normal nuclear matter density. This is a large effect which should have a significant impact on the dynamics of scalar fields in i:uclei. The change of < qq > implies a decreasing pion decay constant in matter, whereas the pion mass remains almost unchanged. This special behaviour is a consequence of the Goldstone boson nature of the pion. For kaons in matter, a distinction has to be made between K + and K-because of their different quark contents. For example, the K-(fis) does not experience Pauli principle effects in nuclear matter to leading order, whereas the K+(fts) does. Model predictions and K +-nucleus scattering phenomenology indicate a very weakly rising K + mass in matter, whereas the K-probably experiences attractions but at a rate which is still under some debate. This is an interesting issue which may be of some relevance to K+/K - production ratios in high energy heavy-ion collisions. Are there observable consequences of the tendency towards chiral re;;toratiot:? Unfortunately, the pion decay constant f,~ "in medium" is not a directly measurable quantity. However, through the laws of chiral symmetry, f~ is tied to the rescaling of other hadronic properties in matter. An important example is the axial charge transition matrix element in heavy nuclei. Some of the hadron masses should rough;y drop like f;. We are quite familiar with the idea that the nucleon mass is replaced by an effective mass M~-< Mr¢. Whether vector meson masses follow a similar rule remains to be explored. Detailed measurements of dilepton spectra following vector meson production in heavy-ion collisions might help to sort tbis out. I would like to thank Gerry Brown, Matthias Lutz, Mannque Rho and Andreas Steiner for many helpful discussions and correspondence. This work is supported in part by DFG grant We 655 / 11 - 1 and by GSI grant OR WelT.
PY - 1993/3/1
Y1 - 1993/3/1
N2 - Recent developments concerning the relevance of chiral symmetry to nuclear physics are summarized. Spontaneous chiral symmetry breaking in QCD implies a non-trivial structure of the vacuum, with a non-vanishing quark condensate 〈qq〉. The magnitude of This condensate decreases with increasing nuclear density, indicating the tendency toward chiral restoration. Possible consequences of this tendency are discussed, such as changes of hadron properties in dense matter. In particular, we study pions and kaons in matter and point out their special features. We also mention recent work concerning axial charge transitions in nuclei.
AB - Recent developments concerning the relevance of chiral symmetry to nuclear physics are summarized. Spontaneous chiral symmetry breaking in QCD implies a non-trivial structure of the vacuum, with a non-vanishing quark condensate 〈qq〉. The magnitude of This condensate decreases with increasing nuclear density, indicating the tendency toward chiral restoration. Possible consequences of this tendency are discussed, such as changes of hadron properties in dense matter. In particular, we study pions and kaons in matter and point out their special features. We also mention recent work concerning axial charge transitions in nuclei.
UR - http://www.scopus.com/inward/record.url?scp=0010083423&partnerID=8YFLogxK
U2 - 10.1016/0375-9474(93)90615-5
DO - 10.1016/0375-9474(93)90615-5
M3 - Article
AN - SCOPUS:0010083423
SN - 0375-9474
VL - 553
SP - 59
EP - 72
JO - Nuclear Physics, Section A
JF - Nuclear Physics, Section A
IS - C
ER -