Dynamical Breaking of Chiral Symmetry

Research Project

Project/Area Number	63540230
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	核・宇宙線・素粒子
Research Institution	National Laboratory for High Energy Physics (KEK)
Principal Investigator	HIGASHIJIMA Kiyoshi National Laboratory for High Energy Physics, Physics Department, Assistant Professor, 物理研究部, 助教授 (10092313)
Project Period (FY)	1988 – 1989
Project Status	Completed (Fiscal Year 1989)
Budget Amount *help	¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1989: ¥300,000 (Direct Cost: ¥300,000) Fiscal Year 1988: ¥300,000 (Direct Cost: ¥300,000)
Keywords	Chiral Symmetry / Quark mass / Spontaneous Breaking of Symmetry / 力学的破れ / ダイナミカルクォークマス / カレントクォークマス
Research Abstract	The aim of this research is to find the mechanism of the spontaneous breaking of chiral symmetry. Effective potential offer the most efficient tool to study spontaneous symmetry breaking. It has been difficult, however, to find the effective potential for local composite operators such as psipsi. A new method is proposed to define the unambiguous effective potential for such local composite operators by taking into account the effects of the Higg's scalar fields together with those of the strong interactions. The mechanism causing the spontaneous breaking of chiral symmetry is extracted from the study of the Nambu-Jona-Lasinio model. When the attractive force between massless quarks and anti-quarks becomes strong enough, a bound state appears in the most attractive channel. This bound state is inevitably a tachyon since the constituent particles are massless, and the vacuum becomes unstable. In order to cure this instability the vacuum rearranges itself to give appropriate mass to the quarks so that the bound state becomes a stable massless boson. This fundamental mechanism is universal and independent of specific models. In fact, we have shown the chiral symmetry breaks down spontaneously by this mechanism in QCD. In so doing it is essential to incorporate the asymptotic free property of the QCD in the Schwinger-Dyson equation in order to obtain the non-trivial continuum limit.