Photonuclear sum rules and the tetrahedral configuration of $^4$He
  Three well known photonuclear sum rules (SR), i.e. the Thomas-Reiche-Kuhn, the bremsstrahlungs and the polarizability SR are calculated for 4He with the realistic nucleon-nucleon potential Argonne V18 and the three-nucleon force Urbana IX. The relation between these sum rules and the corresponding energy weighted integrals of the cross section is discussed. Two additional equivalences for the bremsstrahlungs SR are given, which connect it to the proton-neutron and neutron-neutron distances. Using them, together with our result for the bremsstrahlungs SR, we find a deviation from the tetrahedral symmetry of the spatial configuration of 4He. The possibility to access this deviation experimentally is discussed. 
Doron Gazit, Nir Barnea, Sonia Bacca, Winfried Leidemann and   Giuseppina Orlandini