An exact time-dependent generator coordinate method with projection for spontaneous fission reactions
Microscopic descriptions of fission dynamics through the barrier rely on different theoretical frameworks depending on the fission regime, with the time-dependent generator coordinate method (TDGCM) commonly used for induced fission and semiclassical approaches such as the Wentzel-Kramers-Brillouin (WKB) method widely employed for spontaneous fission. In this work, we develop a fully microscopic approach to spontaneous fission based on an exact formulation of the TDGCM, avoiding both the Gaussian overlap approximation and semiclassical treatments. By combining the exact TDGCM with new projection tools and a quasistatic description of spontaneous fission, we derive spontaneous fission lifetimes from a one-dimensional potential energy surface. A detailed analysis of the model parameters shows that they do not introduce uncontrolled phenomenological effects. Remaining discrepancies with experimental lifetimes are traced to possible limitations of the underlying microscopic interaction and to the choice of basis states in the generator coordinate method. The new framework provides a microscopic description of spontaneous fission with reduced empirical input and offers a pathway toward improved predictions through future developments of nuclear interactions, collective coordinates, and the handling of many-body dynamics.