Implications of PREX-2 on the electric dipole polarizability of neutron-rich nuclei

The nuclear symmetry energy plays a key role in understanding physics of neutron-rich matter from the valley of stability up to neutron-star masses. Analysis of two of the best symmetry energy constraints---the neutron-skin thickness of ${}^{208}$Pb recently extracted from parity-violating electron scattering and the electric dipole polarizability measured in photoabsorption experiments---lead to different conclusions, which highlights a long-standing question in nuclear physics.