Beyond the mean-field: Quantum Monte Carlo approach for finite fermi systems

Large-amplitude fluctuations around the mean-field are important in hot finite Fermi systems. In the quantum Monte Carlo approach these fluctuations are taken into account exactly but often lead to a sign problem. A practical solution to the sign problem in the framework of the nuclear shell model allows realistic calculations in model spaces that are much larger than those that can be treated by conventional diagonalization methods. Recent applications of the Monte Carlo methods for microscopic calculations of collectivity and level densities in heavy nuclei are presented.