Electron angular distributions and circular dichroism effects for double photoionization of polarized atoms

We consider double photoionization (DPI) of a polarized He atom that is in the $n^{1,3}P$-state. For the axially-symmetric polarized $n^{1,3}P$-states and an arbitrary polarization of the photon beam, we have derived {\it ab initio} parametrizations for the transition amplitude and triply differential cross section (TDCS) in terms of scalar products of vectors that enter this problem. As follows from these parametrizations, a non-zero circular dichroism (CD) effect in DPI of a polarized atom exists even at equal energy sharing, in contrast to DPI from unpolarized atoms. Lowest-order perturbative account of electron correlations in the final state, combined with variational account of electron screening in the $2^{1,3}P$-states, is used to analyze the TDCS and CD quantitatively.