Even-parity formulation

Fiveland and lessee [77] and Krebs et al. [79] have recently discussed a modified formulation of the DO approximation. They adapted the even-parity formulation originally discussed by Lewis and Miller [61], They showed that this formulation yields parabolic equations therefore, a boundary value problem is to be solved instead of an initial value problem. Given that several solution techniques are available for the solution of governing equations (particularly in the field of computational fluid dynamics [CFD]), a solution to the RTE can be obtained with little difficulty. This formulation does not necessarily produce more accurate results, and the ray effects still persist. 

Other groups may be handled in a similar manner to O in Example 8.1-1. For improper rotations, the two rules formulated previously hold also for double groups (Box 8.1). If the group contains the inversion operator, even or odd parity is indicated by a superscript of + or —in Bethe s notation and by a subscript g or u in Mulliken-Herzberg notation. 

The conclusion of these works is that the parity (P) invariance and, separately, the charge conjugation (C) invariance are violated in P decay, while the time reversal (T) or combined CP invariance is not. The parity non-invariance (i.e., non-invariance of the Hamiltonian of the weak interaction under space reflection) can be expressed alternativelyby saying that the parity is not conserved. This formulation is a consequence of the fact that the parity P is an observable quantity. The presence of two-pion decay mode in the K° kaon decay implies, however, that even the CP invariance is violated in the weak interaction (Christenson et al. 1964). 

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