Relativistic approach to the nuclear breathing mode

Nuclear compressibility governs fluctuations around the saturation density of nuclear matter, and is therefore crucial for understanding the structure of nuclei as well as of neutron stars. QRPA calculations using a nuclear compression modulus that reproduces the position of the isoscalar giant monopole resonance in ²⁰⁸Pb predict too high an energy for the same excitation in the Sn isotopes. The author shows that the self-consistent inclusion of quasiparticle-vibration coupling beyond QRPA in a relativistic framework can solve the problem. This indicates that a consensus between a softer equation of state extracted from the compressibility of finite nuclei and a stiffer one required by recent analyses of neutron star data can be achieved by systematic incorporation of beyond-QRPA many-body correlations in the theory.