IMPLICATIONS OF PARITY AND TIME-REVERSAL SYMMETRIES IN ATOMS

We have investigated the implications of parity and time-reversal symm etries in atom. The atomic wave function is expressed as a linear comb ination of configuration wave functions. If parity symmetry is violate d, an atomic state no longer has a definite parity such that both elec tronic orbitals and configuration weight coefficients contain parity-n onconserving components. Time-reversal symmetry guarantees that the ra dial wave functions of the large and small components of the Dirac orb ital differ in phase by +/-pi/2, and the parity-conserving and parity- nonconserving components of the Dirac orbital differ in phase by +/-pi /2 as well. In addition, time-reversal symmetry implies that the relat ive phases between parity-conserving configuration weight coefficients are 0 or pi, while the relative phases between parity-conserving and parity-nonconserving configuration weight coefficients are +/-pi/2. Th e absence of permanent electric dipole moments of atoms with definite angular momentum is demonstrated. In addition, the Kramers theorem is elucidated explicitly in the relativistic context. In the multipole ex pansion of the photon field, the relative phases between the expansion coefficients for the transverse electric multipole potentials and for the magnetic or longitudinal electric multipole potentials are +/-pi/ 2. Finally, we show that the relative phases between competing transit ion amplitudes are 0 or pi, which leads to constructive or destructive interferences between competing atomic transitions.