Abstract: |
We analyze status of C, P and T discrete symmetries in application to neutron-antineutron transitions breaking conservation of baryon charge B by two units. At the level of free particles all these symmetries are preserved. This includes P reflection in spite of the opposite internal parities usually ascribed to neutron and antineutron. Explanation, which goes back to the 1937 paper by G. Racah, is based on a definition of parity satisfying P^2=-1, instead of P^2=1,and ascribing P=i to both, neutron and antineutron. We apply this to C, P and T classification of six-quark operators with |\Delta {\cal B} |=2. It allows to specify operators contributing to neutron-antineutron oscillations. Remaining operators contribute to other |\Delta {\cal B} |=2 processes and, in particular, to nuclei instability. |