Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2006-02-01
Phys.Rept. 435 (2006) 157-182
Physics
High Energy Physics
High Energy Physics - Phenomenology
32 pages, 8 figures; v2 revised and expanded; submitted to Phys. Rep
Scientific paper
10.1016/j.physrep.2006.09.004
We study the evidence for and possible origins of parity doubling among the baryons. First we explore the experimental evidence, finding a significant signal for parity doubling in the non-strange baryons, but little evidence among strange baryons. Next we discuss potential explanations for this phenomenon. Possibilities include suppression of the violation of the flavor singlet axial symmetry ($U(1)_{A}$) of QCD, which is broken by the triangle anomaly and by quark masses. A conventional Wigner-Weyl realization of the $SU(2)_{L}\times SU(2)_{R}$ chiral symmetry would also result in parity doubling. However this requires the suppression of families of \emph{chirally invariant} operators by some other dynamical mechanism. In this scenario the parity doubled states should decouple from pions. We discuss other explanations including connections to chiral invariant short distance physics motivated by large $N_{c}$ arguments as suggested by Shifman and others, and intrinsic deformation of relatively rigid highly excited hadrons, leading to parity doubling on the leading Regge trajectory. Finally we review the spectroscopic consequences of chiral symmetry using a formalism introduced by Weinberg, and use it to describe two baryons of opposite parity.
Jaffe Richard L.
Pirjol Dan
Scardicchio Antonello
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