Spontaneous CP violation in the NJL model at theta = pi

Understand

As is well-known, spontaneous CP-violation in the strong interaction is possible at theta = pi, which is commonly referred to as Dashen's phenomenon.

• This phenomenon has been studied extensively using chiral Lagrangians.
• Here the two-flavor NJL model at theta = pi is discussed.
• It turns out that the occurrence of spontaneous CP-violation depends on the strength of the 't Hooft determinant interaction, which describes the effect of instanton interactions.